On 7 August 1942 U.S. Marines landed on Guadalcanal, beginning the Guadalcanal Campaign. The Allies created a combined air formation, the Cactus Air Force, establishing air superiority during daylight hours. The Japanese then resorted to nightly resupply missions which they called "Rat Transportation" (and the Allies called "the Tokyo Express") through New Georgia Sound (a.k.a. "The Slot"). Many pitched battles were fought trying to stop Japanese supplies from getting through. So many ships were lost by both sides during the Guadalcanal campaign that the southern end of New Georgia Sound, the area north of Guadalcanal previously called Savo Sound, became known as "Ironbottom Sound".