One of the most effective German nightfighters was the Ju 88. Its success against Bomber Command was credited to having upward pointed guns that allowed it to attack from below.
Nicknamed Schräge Musik, which means Jazz in German, the attack from below had the advantage that the Ju 88 crew could observe and identify the silhouette of the aircraft against the sky before they attacked.
Belly turrets were not equipped in most British bombers and the Bomber crew could not see the nightfighter against the dark ground, nor defend itself from below.
The nightfighters were careful to aim for the fuel tanks. If they hit the fuselage, exploding bombs could damage the attacker.
Schräge Musik produced devastating results in the winter of 1943-1944. RAF Bomber command was unable to combat what their Bomber crews could not see. Only after inspecting several damaged bombers, were they able to understand that the attacks were coming from below.
Nightfighters tracked their prey by radar. Radar locates objects by transmitting radio pulses and measuring how long it takes for those pulses to be reflected back.