[Indy un-hitches the train to get away before the rear cars explode]
Selous: Next time, wait for my orders!
Indiana Jones: Sorry.
[the explosives go off, destroying the shells, but the cannon is left intact]
Indiana Jones: We have to go back!
Indiana Jones: Go back and get it! We can't let the Germans keep that gun!
[he reverses the locomotive]
Selous: Are you just making this up as you go along?
Indiana Jones: Well... yes.
Selous: Oh. Right, good work!