Yes, tracers were in use during that time. The first tracers were developed by the British in 1915.
Yes, they did have machine guns in WW2
All sides involved did.
The primary one they used was the Vickers machine gun.
The Little Boy and the Fat Man
machine gun
Cars
The Barrett .50 M82A1 and M-107 fires a very powerful rifle bullet, the Browning Machine Gun ( BMG ) .50 Caliber. This cartridge has been the "bread and butter" bullet of the US Military since before the Second World War and its a cartridge that's here to stay.
The machine gun was the pinnacle of arms technology during World War I. The machine gunner would have been the person who rode on the back of a plane and shot at people, while the pilot focused on navigation.
Suppression and enfilading fire.
The machine-gun .
The machine gun changed warfare
Actually, pretty large. The standard machine guns were 8mm Mauser, .303 Enfield, and 30-06. Larger machine guns such as the .50 Browning were also used. To give you an idea of size, a section of a regular pencil about 1 inch long is the size of the small machine gun bullet.