During World War II submarines made up 2% of the US Navy, however they played a large part, sinking over 30% of Japan's naval forces which was essential in preventing merchandise from reaching Japan and in essence cutting it off from the any aid. Before sonar abilities developed, submarine combat was conducted during the daylight hours and at night the submarines would surface or recharge batteries if necessary. The submarine's main weapon consists of a range of torpedoes which can carry large loads of explosives that detonate upon contact. In the Cold War submarines began to develop, and within the United States alone over $2 trillion dollars were spent on the construction on nuclear submarines and took up over a third of the Navy's funds. Despite being more expensive to build initially, in the long term due to small crews and the ability to go for months, even years, without refueling, submarines have turned out to be cheaper to maintain then most ships. Today submarines are an integral part of the US military. Submarines operate free of logistics support for extended periods that can be years on end. During his time in office, Ronald Regan spent billions on the creation of over 600 nuclear submarines which are deployed with each aircraft carrier taskforce. Some follow shipments related to combating the War on Drugs, however most of this force is currently located in the Middle East. Submarines also have commercial uses to map the bottom of the ocean, study oceanography, and work on salvage and rescue missions, however the overall use of these underwater machines has dropped steadily since the end of the Cold War, and the majority of Reagan's 600 nuclear submarines have been scrapped.