 Among these upgrades were improved anti-aircraft defences, radar detectors, better torpedoes, decoys, and "Schnorchel" (snorkels), which allowed U-boats to run underwater off their diesel engines.Germany returned to the offensive in the North Atlantic in September 1943 with initial success, with an attack on convoys ONS 18 and ON 202.A series of battles resulted in fewer victories and more losses for "UbW".