flak shack noun a military hospital or hospital ward where soldiers suffering from war-related psychological problems are treated US,1944
Before we established “flak shacks” for their rehabilitation, it was a very real problem. — Ian Hawkins, B-17soverBerlin, p. 260, 1990
[F]light crews were given a week of rest and recuperation at various rest homes, sometimes known as flak shacks, that were operated by the Red Cross. — Tim Russert, BiggRussandMe, p. 14, 2004