Serviceable Trident missiles can undergo computer diagnostics, compared here with electronic checks on modern cars. Older missiles are described as expendable rounds for testing a submarine's launch system, with firing them avoiding a separate disposal cost. On that account, a missile breaking up after leaving the boat does not necessarily mean the submarine's launch system failed. This is a general explanation of test purposes, without identifying a particular incident or establishing its cause.
Notable Point · 2:08:03-2:09:07
Interpreting Trident missile test failures
A missile failure after launch does not necessarily show that the submarine's launch system failed, especially when an older missile is being expended during the test.