Full Metal Panic: Overload! (2001)

Blurb:
Full Metal Panic: Overload! is not so much a sequel to the first manga series as it is a retelling of the FMP mythos. Originally serialized in a magazine aimed at slightly younger readers, Overload! has the same basic story with a lot more comedy and a lot more explosions! Sousuke has finally lost his mind - and his memory! Rehashing his previous exploits will keep Kaname busy, but it doesn’t take long for the military mind of this soldier to bounce back with a bang - literally! He’s locked, loaded, and back to his old self by first period, as bombs and bullets grace the halls of high school!

Source: www.anisearch.com/manga/3869