It seems to me that a BSD variant would be the strongest choice for warship combat systems. It's incredibly stable, has enormous uptimes, runs on a wide range of CPU architectures, and is modular.
Plus, they could modify the kernels and keep the modifications secret if they wanted to.
And it sounds like they had UNIX software already which would have been easy to port.
Maybe this is a result of SCO Groups behavior. Maybe the heads of BAE figured that it was legally less risky to go with a Microsoft OS because Darl and Co have been threatening everyone with lawsuits over Linux, claim that GCC violates their copyright (BSD needs GCC) and have been making vague threats to the *BSD camp.
[ September 07, 2004: Message edited by: M. O'Brien ]