Must refuel in a friendly city every 4 turns
Bombers have a range of 6 spaces per turn and fuel for 4 turns. If a Bomber remains outside one of your cities for more than four turns, it will run out of fuel and be instantly destroyed when it comes crashing to the ground.
American Bombers are replaced by the Flying Fortress.
English Bombers are replaced by the Lancaster Bomber.
German Bombers are replaced by the Henkel Bomber.
Japanese Bombers are replaced by the Val Bomber.