A launch tube assembly including an aft launch tube portion, a forward launch
tube
portion, and a transfer sleeve having a first end fixed to and adjacent the forward
end of said aft launch tube portion and a second end adjustably receiving the forward
launch tube portion. A forward end of the aft launch tube portion faces a rearward
end of the forward launch tube portion within the transfer sleeve. An adjustable
plenum is present having a volume within the transfer sleeve defined by an adjusted
distance between the facing ends of aft and forward launch tube portions. An end
cap is pinned to a forward end of the forward launch tube portion, a gas generator
housed in the aft launch tube portion, and a countermeasure device is housed in
the forward launch tube portion. An adjustably selected volume of the plenum is
such that a gas generated by the gas generator will enable propulsion of the countermeasure
device at a predetermined acceleration from the forward launch tube portion.