No target attacked. As aircraft was running up to bomb, was attacked by JU88 from port quarter up. Rear gunner opened fire and told the pilot to commence diving to port. JU88continued firing and shells hit the rear turret rendering it u/s and injuring the rear gunner. Mid upper gunner killed probably in the initial burst of fire. The enemy aircraft dived to port and took up position beneath the Lancaster approx 600 feet below. It then continued to move from port to starboard and starboard to port. The front gunner was able to get in several good bursts, the last of which brought sparks from the enemy aircraft which dived and disappeared below. Bomb Aimer pressed bomb release and took jettison action at first indication of tracer but was unaware bombs had not released due to electrical failure. Bombs jettisoned mid-channel.