TROJAN SPIRIT is a communications system operated by U.S. military intelligence, which is approved for handling information of the highest security levels. While the compartmented control system information it handles is principally for intelligence (i.e., TOP SECRET sensitive compartmented intelligence (TS/SCI), it can also be used for the most sensitive command and operations information, at the collateral TOP SECRET level and above. "Spirit" is an acronym for "Special Purpose Intelligence Remote Integrated Terminal (SPIRIT)"
It is a tactical network that allows sharing of this information among appropriate elements in the field, but also provides connectivity to worldwide maximum security networks such as JWICS and specific United States intelligence community networks. While it is tactically used, however, there is a TROJAN Data Network (TDN) operations center at Fort Belvoir, VA, where the central AN/FSQ-144(V) TROJAN CLASSIC equipment is located. There are actually three networks within TDN:
- TDN-1, operating at the SECRET security level between TROJAN Classic facilities, switch extensions, and SPIRITs.
- TDN-2, at the TS/SCI security level. It provides data exchange between selected TROJAN sites requiring access to the National Security Agency network, which is separate from JWICS
- TDN-3, also at the TS/SCI security level, but the gateway to JWICS.
TROJAN SPIRIT is an example of a "stovepiped" system, developed for specific user requirements that could not be met by the general communications systems. As long as security and other operational requirements can be met by enhancing the general systems, the latter approach is desirable, both to reduce costs and to offer the end user more flexibility if the stovepiped equipment is not available. 
Its implementation is evolving as part of the restructuring of the United States Army. Within a division, before the full change to Brigade Combat Teams BCT, there are 17 points that need TS/SCI access. It is expected there will be three such points per BCT.
Originally, each TROJAN SPIRIT node had its own AN/TSQ-190(V) satellite terminal; TROJAN SPIRIT had often been considered synonymous with the combination of satellite and ground communications & security equipment.
TROJAN SPIRIT II is being replaced by the AN/TSQ-226(V)TROJAN SPIRIT LITE. The TROJAN SPIRIT LITE is fielded in four versions, admittedly with the question if 22 cases in V(1), some of which require 4 men to lift, are in fact "lite"::
- (V)1 -a commercial off-the-shelf version in a transit case configuration used to augment Military Intelligence dissemination and communications requirements primarily at corps and division, and some EAC
- (V)2 for the Marines
- (V)2-SBCT (pallet, shelter, ECV, trailer) for Army Brigade Combat Teams
- (V)3 is similar to (V)2 but adds an additional shelter and workstation.
- (V)4 for Echelons above Corps
Over 300 systems are in the field, but the number of new satellite stations is unlikely to increase. With the availability of the Joint Network Node, there would still be a satellite terminal per BCT, but other users in "TS/SCI enclaves" would reach it using secure tunneling through the Joint Network Node. TS/SCI communications require TSEC/KG-175 series (TACLANE) in-line network encryption (INE) devices. These points of access are called WIN intelligence gateways (WIN-IG).
TROJAN SPIRIT was used extensively in Operation DESERT STORM and subsequent operations. In addition to its use with national intelligence systems, it also was used for communications among U.S. Army PROPHET tactical electronic intelligence systems, as well as U.S. Marine Corps field headquarters.
In Bosnia from the mid-nineties, ground stations for the U.S. MQ-1 Predator used TROJAN SPIRIT to send imagery into intelligence networks. The video from this unmanned aerial vehicle was subsequently fed into the Global Broadcast Service communications satellites, to make it available to NATO users that did not have access to compartmented intelligence communications.
TROJAN SPIRIT internally migrated from Asychronous Transfer Mode to Internet Protocol version 4 communications with TROJAN SPIRIT II. To evolve the TROJAN SPIRIT II, the satellite communications had to be upgraded, with more efficient radio modems and TSEC/KIV-19 cryptographic equipment to supplement slower TSEC/KIV-7HS units. These upgrades were selected before the BCT restructuring of the Army, so concentrate on requirements at division, corps, and echelons above corps. 
TROJAN SPIRIT II, however, was replaced by TROJAN SPIRIT LITE. 
The next step is to integrate TROJAN SPIRIT II with common networks. TROJAN SPIRIT already goes through JNN, and JNN is compatible with Warfighter Information Network-Tactical.
- U.S. Army (April 2004), Field Manual 6-02.45 (FM 11-45), Signal Support to Theater Operations,p. 2-4
- U.S. Army (September 2006), FMI 6-02.60 Tactics, Techniques, and Procedures (TTPs) for the Joint Network Node-Network (JNN-N),pp. 1-3 to 1-4
- (V) denotes that the system is modular and can be field modified
- "AN/TSQ-190 TROJAN / TROJAN SPIRIT II Communications Central", Globalsecurity
- Nicholas Yuran (November 2008), "COMM OPS: Intelligence In Networking", MilsatMagazine
- Scott Long (Winter 1999), "Trojan Spirit to Warfighter Information Network migration plan: a reality", Army Communicator
- Gourley, Scott R (July 2003), "TROJAN SPIRIT LITE: Bridging the legacy to objective information gap", Army