EXHIBIT 10.56

                     SUPPLEMENTAL INDENTURE TO BE DELIVERED
                          BY GUARANTEEING SUBSIDIARIES

     Supplemental Indenture (this "Supplemental Indenture"), dated as of August
5, 2004, among L-3 Communications Corporation (or its permitted successor), a
Delaware corporation (the "Company"), each subsidiary of the Company signatory
hereto (each, a "Guaranteeing Subsidiary", and collectively, the "Guaranteeing
Subsidiaries"), and The Bank of New York, as trustee under the indenture
referred to below (the "Trustee").

                              W I T N E S S E T H:
                              - - - - - - - - - -

         WHEREAS, the Company has heretofore executed and delivered to the
Trustee an indenture (as amended, the "Indenture"), dated as of December 11,
1998 providing for the issuance of an aggregate principal amount of up to
$300,000,000 of 8% Senior Subordinated Notes due 2008 (the "Notes");

         WHEREAS, the Indenture provides that under certain circumstances the
Guaranteeing Subsidiaries shall execute and deliver to the Trustee a
supplemental indenture pursuant to which the Guaranteeing Subsidiaries shall
unconditionally guarantee all of the Company's Obligations under the Notes and
the Indenture on the terms and conditions set forth herein (the "Subsidiary
Guarantee"); and

         WHEREAS, pursuant to Sections 4.13 and 9.01 of the Indenture, the
Trustee is authorized to execute and deliver this Supplemental Indenture.

         NOW THEREFORE, in consideration of the foregoing and for other good and
valuable consideration, the receipt of which is hereby acknowledged, the
Guaranteeing Subsidiaries and the Trustee mutually covenant and agree for the
equal and ratable benefit of the Holders of the Notes as follows:


         1. CAPITALIZED TERMS. Capitalized terms used herein without definition
shall have the meanings assigned to them in the Indenture.

         2. AGREEMENT TO GUARANTEE. Each Guaranteeing Subsidiary hereby agrees
as follows:

            (a)   Each Guaranteeing Subsidiary, jointly and severally with all
                  other current and future guarantors of the Notes
                  (collectively, the "Guarantors" and each, a "Guarantor"),
                  unconditionally guarantees to each Holder of a Note
                  authenticated and delivered by the Trustee and to the Trustee
                  and its successors and assigns, regardless of the validity and
                  enforceability of the Indenture, the Notes or the Obligations
                  of the Company under the Indenture or the Notes, that:

                  (i)   the principal of, premium and interest on the Notes will
                        be promptly paid in full when due, whether at maturity,
                        by


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                        acceleration, redemption or otherwise, and interest on
                        the overdue principal of, premium and interest on the
                        Notes, to the extent lawful, and all other Obligations
                        of the Company to the Holders or the Trustee thereunder
                        or under the Indenture will be promptly paid in full,
                        all in accordance with the terms thereof; and

                  (ii)  in case of any extension of time for payment or renewal
                        of any Notes or any of such other Obligations, that the
                        same will be promptly paid in full when due in
                        accordance with the terms of the extension or renewal,
                        whether at stated maturity, by acceleration or
                        otherwise.

            (b)   Notwithstanding the foregoing, in the event that this
                  Subsidiary Guarantee would constitute or result in a violation
                  of any applicable fraudulent conveyance or similar law of any
                  relevant jurisdiction, the liability of each Guaranteeing
                  Subsidiary under this Supplemental Indenture and its
                  Subsidiary Guarantee shall be reduced to the maximum amount
                  permissible under such fraudulent conveyance or similar law.

         3. EXECUTION AND DELIVERY OF SUBSIDIARY GUARANTEES.

            (a)   To evidence its Subsidiary Guarantee set forth in this
                  Supplemental Indenture, each Guaranteeing Subsidiary hereby
                  agrees that a notation of such Subsidiary Guarantee
                  substantially in the form of Exhibit F to the Indenture shall
                  be endorsed by an officer of such Guaranteeing Subsidiary on
                  each Note authenticated and delivered by the Trustee after the
                  date hereof.

            (b)   Notwithstanding the foregoing, each Guaranteeing Subsidiary
                  hereby agrees that its Subsidiary Guarantee set forth herein
                  shall remain in full force and effect notwithstanding any
                  failure to endorse on each Note a notation of such Subsidiary
                  Guarantee.

            (c)   If an Officer whose signature is on this Supplemental
                  Indenture or on the Subsidiary Guarantee no longer holds that
                  office at the time the Trustee authenticates the Note on which
                  a Subsidiary Guarantee is endorsed, the Subsidiary Guarantee
                  shall be valid nevertheless.

            (d)   The delivery of any Note by the Trustee, after the
                  authentication thereof under the Indenture, shall constitute
                  due delivery of the Subsidiary Guarantee set forth in this
                  Supplemental Indenture on behalf of each Guaranteeing
                  Subsidiary.

            (e)   Each Guaranteeing Subsidiary hereby agrees that its
                  obligations hereunder shall be unconditional, regardless of
                  the validity,


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                  regularity or enforceability of the Notes or the Indenture,
                  the absence of any action to enforce the same, any waiver or
                  consent by any Holder of the Notes with respect to any
                  provisions of the Notes or the Indenture, the recovery of any
                  judgment against the Company, any action to enforce the same
                  or any other circumstance which might otherwise constitute a
                  legal or equitable discharge or defense of a guarantor.

            (f)   Each Guaranteeing Subsidiary hereby waives diligence,
                  presentment, demand of payment, filing of claims with a court
                  in the event of insolvency or bankruptcy of the Company, any
                  right to require a proceeding first against the Company,
                  protest, notice and all demands whatsoever and covenants that
                  its Subsidiary Guarantee made pursuant to this Supplemental
                  Indenture will not be discharged except by complete
                  performance of the obligations contained in the Notes and the
                  Indenture.

            (g)   If any Holder or the Trustee is required by any court or
                  otherwise to return to the Company or any Guaranteeing
                  Subsidiary, or any Custodian, Trustee, liquidator or other
                  similar official acting in relation to either the Company or
                  such Guaranteeing Subsidiary, any amount paid by either to the
                  Trustee or such Holder, the Subsidiary Guarantee made pursuant
                  to this Supplemental Indenture, to the extent theretofore
                  discharged, shall be reinstated in full force and effect.

            (h)   Each Guaranteeing Subsidiary agrees that it shall not be
                  entitled to any right of subrogation in relation to the
                  Holders in respect of any obligations guaranteed hereby until
                  payment in full of all obligations guaranteed hereby. Each
                  Guaranteeing Subsidiary further agrees that, as between such
                  Guaranteeing Subsidiary, on the one hand, and the Holders and
                  the Trustee, on the other hand:

                  (i)   the maturity of the obligations guaranteed hereby may be
                        accelerated as provided in Article 6 of the Indenture
                        for the purposes of the Subsidiary Guarantee made
                        pursuant to this Supplemental Indenture, notwithstanding
                        any stay, injunction or other prohibition preventing
                        such acceleration in respect of the obligations
                        guaranteed hereby; and

                  (ii)  in the event of any declaration of acceleration of such
                        obligations as provided in Article 6 of the Indenture,
                        such obligations (whether or not due and payable) shall
                        forthwith become due and payable by such Guaranteeing
                        Subsidiary for the purpose of the Subsidiary Guarantee
                        made pursuant to this Supplemental Indenture.

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            (i)   Each Guaranteeing Subsidiary shall have the right to seek
                  contribution from any other non-paying Guaranteeing Subsidiary
                  so long as the exercise of such right does not impair the
                  rights of the Holders or the Trustee under the Subsidiary
                  Guarantee made pursuant to this Supplemental Indenture.

         4. GUARANTEEING SUBSIDIARIES MAY CONSOLIDATE, ETC. ON CERTAIN TERMS.

            (a)   Except as set forth in Articles 4 and 5 of the Indenture,
                  nothing contained in the Indenture, this Supplemental
                  Indenture or in the Notes shall prevent any consolidation or
                  merger of any Guaranteeing Subsidiary with or into the Company
                  or any other Guarantor or shall prevent any transfer, sale or
                  conveyance of the property of any Guaranteeing Subsidiary as
                  an entirety or substantially as an entirety, to the Company or
                  any other Guarantor.

            (b)   Except as set forth in Article 4 of the Indenture, nothing
                  contained in the Indenture, this Supplemental Indenture or in
                  the Notes shall prevent any consolidation or merger of any
                  Guaranteeing Subsidiary with or into a corporation or
                  corporations other than the Company or any other Guarantor (in
                  each case, whether or not affiliated with such Guaranteeing
                  Subsidiary), or successive consolidations or mergers in which
                  a Guaranteeing Subsidiary or its successor or successors shall
                  be a party or parties, or shall prevent any sale or conveyance
                  of the property of any Guaranteeing Subsidiary as an entirety
                  or substantially as an entirety, to a corporation other than
                  the Company or any other Guarantor (in each case, whether or
                  not affiliated with such Guaranteeing Subsidiary) authorized
                  to acquire and operate the same; provided, however, that each
                  Guaranteeing Subsidiary hereby covenants and agrees that (i)
                  subject to the Indenture, upon any such consolidation, merger,
                  sale or conveyance, the due and punctual performance and
                  observance of all of the covenants and conditions of the
                  Indenture and this Supplemental Indenture to be performed by
                  such Guaranteeing Subsidiary, shall be expressly assumed (in
                  the event that such Guaranteeing Subsidiary is not the
                  surviving corporation in the merger), by supplemental
                  indenture satisfactory in form to the Trustee, executed and
                  delivered to the Trustee, by the corporation formed by such
                  consolidation, or into which such Guaranteeing Subsidiary
                  shall have been merged, or by the corporation which shall have
                  acquired such property and (ii) immediately after giving
                  effect to such consolidation, merger, sale or conveyance no
                  Default or Event of Default exists.


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            (c)   In case of any such consolidation, merger, sale or conveyance
                  and upon the assumption by the successor corporation, by
                  supplemental indenture, executed and delivered to the Trustee
                  and satisfactory in form to the Trustee, of the Subsidiary
                  Guarantee made pursuant to this Supplemental Indenture and the
                  due and punctual performance of all of the covenants and
                  conditions of the Indenture and this Supplemental Indenture to
                  be performed by each Guaranteeing Subsidiary, such successor
                  corporation shall succeed to and be substituted for such
                  Guaranteeing Subsidiary with the same effect as if it had been
                  named herein as the Guaranteeing Subsidiary. Such successor
                  corporation thereupon may cause to be signed any or all of the
                  Subsidiary Guarantees to be endorsed upon the Notes issuable
                  under the Indenture which theretofore shall not have been
                  signed by the Company and delivered to the Trustee. All the
                  Subsidiary Guarantees so issued shall in all respects have the
                  same legal rank and benefit under the Indenture and this
                  Supplemental Indenture as the Subsidiary Guarantees
                  theretofore and thereafter issued in accordance with the terms
                  of the Indenture and this Supplemental Indenture as though all
                  of such Subsidiary Guarantees had been issued at the date of
                  the execution hereof.

         5. RELEASES.

            (a)   Concurrently with any sale of assets (including, if
                  applicable, all of the Capital Stock of a Guaranteeing
                  Subsidiary), all Liens, if any, in favor of the Trustee in the
                  assets sold thereby shall be released; provided that in the
                  event of an Asset Sale, the Net Proceeds from such sale or
                  other disposition are treated in accordance with the
                  provisions of Section 4.10 of the Indenture. If the assets
                  sold in such sale or other disposition include all or
                  substantially all of the assets of a Guaranteeing Subsidiary
                  or all of the Capital Stock of a Guaranteeing Subsidiary, then
                  the Guaranteeing Subsidiary (in the event of a sale or other
                  disposition of all of the Capital Stock of such Guaranteeing
                  Subsidiary) or the Person acquiring the property (in the event
                  of a sale or other disposition of all or substantially all of
                  the assets of such Guaranteeing Subsidiary) shall be released
                  from and relieved of its obligations under this Supplemental
                  Indenture and its Subsidiary Guarantee made pursuant hereto;
                  provided that in the event of an Asset Sale, the Net Proceeds
                  from such sale or other disposition are treated in accordance
                  with the provisions of Section 4.10 of the Indenture. Upon
                  delivery by the Company to the Trustee of an Officers'
                  Certificate to the effect that such sale or other disposition
                  was made by the Company or the Guaranteeing Subsidiary, as the
                  case may be, in accordance with the provisions of the
                  Indenture and this Supplemental Indenture, including without
                  limitation, Section 4.10 of the

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                  Indenture, the Trustee shall execute any documents reasonably
                  required in order to evidence the release of the Guaranteeing
                  Subsidiary from its obligations under this Supplemental
                  Indenture and its Subsidiary Guarantee made pursuant hereto.
                  If the Guaranteeing Subsidiary is not released from its
                  obligations under its Subsidiary Guarantee, it shall remain
                  liable for the full amount of principal of and interest on the
                  Notes and for the other obligations of such Guaranteeing
                  Subsidiary under the Indenture as provided in this
                  Supplemental Indenture.

            (b)   Upon the designation of a Guaranteeing Subsidiary as an
                  Unrestricted Subsidiary in accordance with the terms of the
                  Indenture, such Guaranteeing Subsidiary shall be released and
                  relieved of its obligations under its Subsidiary Guarantee and
                  this Supplemental Indenture. Upon delivery by the Company to
                  the Trustee of an Officers' Certificate and an Opinion of
                  Counsel to the effect that such designation of such
                  Guaranteeing Subsidiary as an Unrestricted Subsidiary was made
                  by the Company in accordance with the provisions of the
                  Indenture, including without limitation Section 4.07 of the
                  Indenture, the Trustee shall execute any documents reasonably
                  required in order to evidence the release of such Guaranteeing
                  Subsidiary from its obligations under its Subsidiary
                  Guarantee. Any Guaranteeing Subsidiary not released from its
                  obligations under its Subsidiary Guarantee shall remain liable
                  for the full amount of principal of and interest on the Notes
                  and for the other obligations of any Guaranteeing Subsidiary
                  under the Indenture as provided herein.

         6. NO RECOURSE AGAINST OTHERS. No past, present or future director,
officer, employee, incorporator, stockholder or agent of any Guaranteeing
Subsidiary, as such, shall have any liability for any obligations of the Company
or any Guaranteeing Subsidiary under the Notes, any Subsidiary Guarantees, the
Indenture or this Supplemental Indenture or for any claim based on, in respect
of, or by reason of, such obligations or their creation. Each Holder of the
Notes by accepting a Note waives and releases all such liability. The waiver and
release are part of the consideration for issuance of the Notes. Such waiver may
not be effective to waive liabilities under the federal securities laws and it
is the view of the Commission that such a waiver is against public policy.

         7. SUBORDINATION OF SUBSIDIARY GUARANTEES; ANTI-LAYERING. No
Guaranteeing Subsidiary shall incur, create, issue, assume, guarantee or
otherwise become liable for any Indebtedness that is subordinate or junior in
right of payment to any Senior Debt of a Guaranteeing Subsidiary and senior in
any respect in right of payment to any of the Subsidiary Guarantees.
Notwithstanding the foregoing sentence, the Subsidiary Guarantee of each
Guaranteeing Subsidiary shall be subordinated to the prior payment in full of
all Senior Debt of that Guaranteeing Subsidiary (in the same manner and to the
same extent that the Notes are subordinated to Senior Debt), which shall include
all guarantees of Senior Debt.

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         8. THIS SUPPLEMENTAL INDENTURE SHALL BE GOVERNED BY, AND CONSTRUED IN
ACCORDANCE WITH, THE LAWS OF THE STATE OF NEW YORK.

         9. COUNTERPARTS. The parties may sign any number of copies of this
Supplemental Indenture. Each signed copy shall be an original, but all of them
together represent the same agreement.

         10. EFFECT OF HEADINGS. The Section headings herein are for convenience
only and shall not affect the construction hereof.

         11. THE TRUSTEE. The Trustee shall not be responsible in any manner
whatsoever for or in respect of the validity or sufficiency of this Supplemental
Indenture or for or in respect of the recitals contained herein, all of which
recitals are made solely by the Guaranteeing Subsidiaries and the Company.


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         IN WITNESS WHEREOF, the parties hereto have caused this Supplemental
Indenture to be duly executed, all as of the date first above written.



Dated: August 5, 2004               L-3 COMMUNICATIONS CORPORATION


                                    By: /s/ Christopher C. Cambria
                                        ----------------------------------------
                                        Name:  Christopher C. Cambria
                                        Title: Senior Vice President, Secretary
                                               and General Counsel





Dated: August 5, 2004         APCOM, INC., a Maryland corporation
                              BROADCAST SPORTS INC., a Delaware corporation
                              L-3 COMMUNICATIONS CSI, INC., a California
                                corporation
                              ELECTRODYNAMICS, INC., an Arizona corporation
                              HENSCHEL INC., a Delaware corporation
                              HYGIENETICS ENVIRONMENTAL SERVICES, INC., a
                                Delaware corporation
                              INTERSTATE ELECTRONICS CORPORATION, a California
                                corporation
                              KDI PRECISION PRODUCTS, INC., a Delaware
                                corporation
                              L-3 COMMUNICATIONS AEROMET, INC., an Oregon
                                corporation
                              L-3 COMMUNICATIONS VERTEX AEROSPACE LLC, a
                                Delaware limited liability company
                              L-3 COMMUNICATIONS AIS GP CORPORATION, a Delaware
                                corporation
                              L-3 COMMUNICATIONS AVIONICS SYSTEMS, INC., a
                                Delaware corporation
                              L-3 COMMUNICATIONS AVYSIS CORPORATION, a Texas
                                corporation
                              L-3 COMMUNICATIONS AYDIN CORPORATION, a Delaware
                                corporation
                              L-3 COMMUNICATIONS ESSCO, INC., a Delaware
                                corporation
                              L-3 COMMUNICATIONS FLIGHT INTERNATIONAL AVIATION
                                LLC, a Delaware limited liability company
                              L-3 COMMUNICATIONS FLIGHT CAPITAL LLC, a Delaware
                                limited liability company
                              L-3 COMMUNICATIONS GOVERNMENT SERVICES, INC., a
                                Virginia corporation
                              L-3 COMMUNICATIONS ILEX SYSTEMS, INC., a Delaware
                                corporation
                              L-3 COMMUNICATIONS INTEGRATED SYSTEMS L.P., a
                                Delaware limited partnership
                              L-3 COMMUNICATIONS INVESTMENTS INC., a Delaware
                                corporation
                              L-3 COMMUNICATIONS KLEIN ASSOCIATES, INC., a
                                Delaware corporation
                              L-3 COMMUNICATIONS MAS (US) CORPORATION, a
                                Delaware corporation
                              L-3 COMMUNICATIONS SECURITY AND DETECTION SYSTEMS,
                                INC., a Delaware corporation
                              L-3 COMMUNICATIONS SECURITY SYSTEMS CORPORATION, a
                                Delaware corporation
                              L-3 COMMUNICATIONS STORM CONTROL SYSTEMS, INC., a
                                California corporation



                              L-3 COMMUNICATIONS VECTOR INTERNATIONAL AVIATION
                                LLC, a Delaware limited liability company
                              L-3 COMMUNICATIONS WESTWOOD CORPORATION, a Nevada
                                corporation
                              MCTI ACQUISITION CORPORATION, a Maryland
                                corporation
                              MICRODYNE COMMUNICATIONS TECHNOLOGIES
                                INCORPORATED, a Maryland corporation
                              MICRODYNE CORPORATION, a Maryland corporation
                              MICRODYNE OUTSOURCING INCORPORATED, a Maryland
                                corporation
                              MPRI, INC., a Delaware corporation
                              PAC ORD INC., a Delaware corporation
                              POWER PARAGON, INC., a Delaware corporation
                              SHIP ANALYTICS, INC., a Connecticut corporation
                              SHIP ANALYTICS INTERNATIONAL, INC., a Delaware
                                corporation
                              SHIP ANALYTICS USA, INC., a Connecticut
                                corporation
                              SPD ELECTRICAL SYSTEMS, INC., a Delaware
                                corporation
                              SPD SWITCHGEAR INC., a Delaware corporation
                              SYCOLEMAN CORPORATION, a Florida corporation
                              TROLL TECHNOLOGY CORPORATION, a California
                                corporation
                              WESCAM AIR OPS INC., a Delaware corporation
                              WESCAM AIR OPS LLC, a Delaware limited liability
                                company
                              WESCAM HOLDINGS (US) INC., a Delaware corporation
                              WESCAM INCORPORATED, a Florida corporation
                              WESCAM LLC, a Delaware limited liability company
                              WESCAM SONOMA INC., a California corporation
                              WOLF COACH, INC., a Massachusetts corporation As
                                Guaranteeing Subsidiaries

                                       By: /s/ Christopher C. Cambria
                                           --------------------------
                                           Name:  Christopher C. Cambria
                                           Title: Vice President, Secretary





Dated: August 5, 2004                    THE BANK OF NEW YORK,
                                         as Trustee


                                         By: /s/ Robert A. Massimillo
                                             ------------------------
                                             Name:  Robert A. Massimillo
                                             Title: Vice President