(2) Described as a "software-defined radio" JTRS is envisioned tofunction more like a computer than a conventional radio and is to be upgraded and modified tooperate with other communications systems by the addition of software as opposed to redesigninghardware - a more costly and time-consuming process. JTRS Clusters
a. Security for JTRS has emerged as asignificant developmental difficulty. (27) 
Interoperability with Legacy Radio Systems. The Army's FCS program consistsof four "spin outs" -- formerly known as spirals -- that will introduce FCS technologies and systemsto the current force. (55) Preceding the JTRSprogram restructuring, Boeing and Science Applications International Corporation (SAIC) -- whoserve as lead systems integrators for the entire 18 system FCS program -- announced in June 2004that Cluster One and Five programs would be restructured to better meet the needs of the FCSprogram. Issues for Congress

The Viability of the Cluster One Program. It can be argued that network security would take on an even a more significant role in FCSthan compared to the Army's current force.
The Joint Tactical Radio System (JTRS) is a Department of Defense (DOD) program thatwould play a significant role in the U.S Army's proposed Future Combat System (FCS) program. (For a more detailed description of the FCS program see CRS Report RL32888 , The Army's FutureCombat System(FCS): Background and Issues for Congress , by [author name scrubbed].) JTRS,envisioned as a family of software programmable radios, has been described as the "backbone" ofthe FCS and is intended to link the 18 manned and unmanned systems that would constitute FCS.Two JTRS sub-programs managed by the Army -- Cluster One and Cluster Five -- have experienceddevelopmental difficulties, delays, and cost overruns which calls into question their viability. Thisreport will be updated on a periodic basis.