SUPPLEMENTAL INDENTURE TO THE MAY 2003 INDENTURE

                                                                   Exhibit 10.55

                     SUPPLEMENTAL INDENTURE TO BE DELIVERED
                          BY GUARANTEEING SUBSIDIARIES

     Supplemental Indenture (this "Supplemental Indenture"), dated as of January
14, 2005, among L-3 Communications Corporation (or its permitted successor), a
Delaware corporation (the "Company"), each a direct or indirect 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 (the "Indenture"), dated as of May 21, 2003 providing for
the issuance of an unlimited amount of 6 1/8% Senior Subordinated Notes due 2013
(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 (as defined in the
Indenture) under the Notes and the Indenture on the terms and conditions set
forth herein (the "Subsidiary Guarantee"); and

         WHEREAS, pursuant to Section 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) Such 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, interest and Additional Amounts,
                    if any, on the Notes will be promptly paid in full when due,
                    whether at maturity, by acceleration, redemption or
                    otherwise, and interest on the overdue principal of,


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                    premium, interest and Additional Amounts, if any, 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 such 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, such 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, such 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,
                regularity or enforceability of the Notes or the Indenture, the
                absence of any action to enforce the same, any waiver or consent


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                by any Holder of the Notes with respect to any provisions hereof
                or thereof, 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.

            (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



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               the Holders or the Trustee under the Subsidiary Guarantee made
               pursuant to this Supplemental Indenture.

          4.   GUARANTEEING SUBSIDIARY 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 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 a corporation or
                corporations other than the Company or any other Guarantor (in
                each case, whether or not affiliated with the 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