London’s 5 AA guns should be able to role once against each of three attacking German fighters in an amphibious assault then for a maximum of 15 die rolls. 5 AA guns each firing 3 times against each of 3 attacking air units.
the 5 London AA guns could generate no more than 3 die rolls against the 3 German airplanes.
So … which is the correct interpretation?
In the Alpha+3 rules, London begins the game with 4 AA guns ( not sure if your scenario had the UK purchasing one or not, but just wanted to point that out)