3
I believe there are about 65 left in service.
3 u.s bombers disapeared during world war 2
There are many single engine aircraft used as dive bombers and torpedo bombers that could be cited if this were the aim of the question - was it?
1
There are only 2 Martin Mars Water Bombers left in the world. Both are based in Port Alberni on Sproat Lake, in British Columbia Canada. One is named Hawaii Mars, the other named Philippine Mars.
That varied depending on the airplane, bombers could have many.
There 3 planes, the Enola gay and two bombers for escorting.
according to wikipedia, 12,731
7,377 Lancaster bombers were built.
Many airplanes were used in WW1. The British had at least 12 kinds of fighters, 10 12 kinds of bombers and many 'observation aircraft. The Germans had many more kinds of fighters , but fewer bombers. The French had many fighters and a few different bombers. Altogether at least 85-100 different aircraft
At the height of the Luftwaffe's power they had about 2,800 bombers. Almost all of these were what the Allies would class as 'light bombers'.