Simpson Thacher & Bartlett
                              425 Lexington Avenue
                            New York, New York 10017






                                                           September 18, 2002


L-3 COMMUNICATIONS CORPORATION
600 Third Avenue, 34th Floor
New York, NY 10016


Ladies and Gentlemen:


                  We have acted as counsel to L-3 Communications Corporation, a
Delaware corporation (the "Company"), and to the Delaware subsidiaries of the
Company named on Schedule I attached hereto (each, a "Delaware Guarantor" and
collectively, the "Delaware Guarantors") and to the non-Delaware subsidiaries of
the Company named on Schedule II attached hereto (each, a "Non-Delaware
Guarantor" and collectively, the "Non-Delaware Guarantors," taken together with
the Delaware Guarantors, the "Guarantors"), in connection with the Registration
Statement on Form S-4 (the "Registration Statement") filed by the Company and
the Guarantors with the Securities and Exchange Commission (the "Commission")
under the Securities Act of 1933, as amended, relating to the issuance by the
Company of $750,000,000 aggregate principal amount of 7 5/8% Series B Senior
Subordinated Notes Due 2012 (the "Exchange Notes") and the issuance by the
Guarantors of guarantees (the "Guarantees"), with respect to the Exchange Notes.
The Exchange Notes and the Guarantees will be issued under an indenture (the
"Indenture") among the Company, the Guarantors (other than MCTI Acquisition






                                       2                      September 18, 2002


Corporation and L-3 Communications Security and Detection Systems Corporation
Delaware) and the Bank of New York, as Trustee (the "Trustee") and a
supplemental indenture among the Company, the Guarantors and the Trustee. The
Exchange Notes will be offered by the Company in exchange for $750,000,000
aggregate principal amount of its outstanding 7 5/8% Senior Subordinated Notes
due 2008.

                  We have examined the Registration Statement and the Indenture,
which has been filed with the Commission as an exhibit to the Registration
Statement. We also have examined the originals, or duplicates or certified or
conformed copies, of such records, agreements, instruments and other documents
and have made such other and further investigations as we have deemed relevant
and necessary in connection with the opinions expressed herein. As to questions
of fact material to this opinion, we have relied upon certificates of public
officials and of officers and representatives of the Company and the Guarantors.

                  In rendering the opinions set forth below, we have assumed the
genuineness of all signatures, the legal capacity of natural persons, the due
incorporation of the Non-Delaware Guarantors, the authenticity of all documents
submitted to us as originals, the conformity to original documents of all
documents submitted to us as duplicates or certified or conformed copies, and
the authenticity of the originals of such latter documents. We also have assumed
that the Indenture is the valid and legally binding obligation of the Trustee.
We have assumed further that (a) the Non-Delaware Guarantors have duly
authorized, executed and delivered the Indenture, (b) execution, delivery and
performance by the Non-Delaware Guarantors of the Indenture, the Exchange Notes
and the Guarantees do not and will not violate the laws of the states of
incorporation of the respective Non-Delaware Guarantors or any other applicable
laws






                              3                               September 18, 2002


(excepting the laws of the State of New York and the Federal laws of the United
States) and (c) each of the Non-Delaware Guarantors is validly existing under
the laws of their respective jurisdiction of organization.

                  Based upon the foregoing, and subject to the qualifications
and limitations stated herein, we are of the opinion that:

                       1.  When the Exchange Notes have been duly executed,
         authenticated, issued and delivered in accordance with the provisions
         of the Indenture upon the exchange, the Exchange Notes will constitute
         valid and legally binding obligations of the Company enforceable
         against the Company in accordance with their terms.

                       2.  When (a) the Exchange Notes have been duly executed,
         authenticated, issued and delivered in accordance with the provisions
         of the Indenture upon the exchange and (b) the Guarantees have been
         duly indorsed on the Exchange Notes, the Guarantees will constitute
         valid and legally binding obligations of the Guarantors enforceable
         against the Guarantors in accordance with their terms.

                  Our opinion set forth above is subject to the effects of (1)
bankruptcy, insolvency, fraudulent conveyance, reorganization, moratorium and
other similar laws relating to or affecting creditors' rights generally, (2)
general equitable principles (whether considered in a proceeding in equity or at
law) and (3) an implied covenant of good faith and fair dealing.

                  We are members of the Bar of the State of New York and we do
not express any opinion herein concerning any law other than the law of the
State of New York, the Federal law of the United States, the Delaware General
Corporation Law and the Delaware Revised Uniform Limited Partnership Act.







                              4                               September 18, 2002


                  We hereby consent to the filing of this opinion letter as
Exhibit 5 to the Registration Statement and to the use of our name under the
caption "Legal Matters" in the Prospectus included in the Registration
Statement.



                                Very truly yours,

                                /s/ Simpson Thacher & Bartlett

                                SIMPSON THACHER & BARTLETT









                              5                               September 18, 2002


                                   SCHEDULE I

HYGIENETICS ENVIRONMENTAL SERVICES, INC., a Delaware Corporation
L-3 COMMUNICATIONS ILEX SYSTEMS, INC., a Delaware Corporation
L-3 COMMUNICATIONS SPD TECHNOLOGIES, INC., a Delaware Corporation
L-3 COMMUNICATIONS ESSCO, INC., a Delaware Corporation
SPD ELECTRICAL SYSTEMS, INC., a Delaware Corporation
SPD SWITCHGEAR, INC., a Delaware Corporation
PAC ORD, INC., a Delaware Corporation
HENSCHEL, INC., a Delaware Corporation
SPD HOLDINGS, INC., a Delaware Corporation
POWER PARAGON, INC., a Delaware Corporation
L-3 COMMUNICATIONS AYDIN CORPORATION, a Delaware Corporation
L-3 COMMUNICATIONS INTEGRATED SYSTEMS L.P., a Delaware Limited Partnership
L-3 COMMUNICATIONS AIS GP CORPORATION, a Delaware Corporation
L-3 COMMUNICATIONS INVESTMENTS, INC., a Delaware Corporation
L-3 COMMUNICATIONS SECURITY AND DETECTION SYSTEMS CORPORATION
      DELAWARE, a Delaware Corporation
MPRI, INC., a Delaware Corporation
KDI PRECISION PRODUCTS, INC., a Delaware Corporation











                              6                               September 18, 2002


                                   SCHEDULE II

SOUTHERN CALIFORNIA MICROWAVE, INC., a California Corporation
L-3 COMMUNICATIONS STORM CONTROL SYSTEMS, INC., a California Corporation
MICRODYNE CORPORATION, a Maryland Corporation
ELECTRODYNAMICS, INC., an Arizona Corporation
INTERSTATE ELECTRONICS CORPORATION, a California Corporation
COLEMAN RESEARCH CORPORATION, a Florida Corporation
EER SYSTEMS, INC., a Virginia Corporation
L-3 COMMUNICATIONS ANALYTICS CORPORATION, a California Corporation
AMI INSTRUMENTS, INC., an Oklahoma Corporation
L-3 COMMUNICATIONS ATLANTIC SCIENCE AND TECHNOLOGY CORPORATION, a
      New Jersey Corporation
MICRODYNE COMMUNICATIONS TECHNOLOGIES INCORPORATED, a Maryland
      Corporation
APCOM, INC., a Maryland Corporation
CELERITY SYSTEMS INCORPORATED, a California Corporation
MCTI ACQUISITION CORPORATION, a Maryland Corporation
MICRODYNE OUTSOURCING INCORPORATED, a Maryland Corporation