General-purpose bombs (GP) use a thick-walled metal casing with explosive filler (typically TNT, Composition B, or Tritonal in NATO or United States service) composing about 30% to 40% of the bombs' total weight. The British term for a bomb of this type is "medium case" or "medium capacity" (MC). The GP bomb is a common weapon of fighter bomber and attack aircraft because it is useful for a variety of tactical applications and relatively cheap.
General-purpose bombs are often identified by their weight (e.g., 500 lb). In many cases this is strictly a nominal weight, or caliber, and the actual weight of each individual weapon may vary depending on its retardation, fusing, carriage, and guidance systems. For example, the actual weight of a U.S. M117 bomb, nominally 750 lb , is typically around 820 lb.
Most modern air-dropped GP bombs are designed to minimize drag for external carriage on aircraft lacking bomb bays.
In low-altitude attacks, there is a danger of the attacking aircraft being caught in the blast of its own weapons. To address this problem, GP bombs are often fitted with retarders, parachutes or pop-out fins that slow the bombs descent to allow the aircraft time to escape the detonation.
GP bombs can be fitted with a variety of fuses and fins for different uses. One notable example is the "daisy cutter" fuse used in Vietnam War era American weapons, an extended probe designed to ensure that the bomb would detonate on contact (even with foliage) rather than burying itself in earth or mud, which would reduce its effectiveness. (This was not the first instance of such devices. As early as World War II, the Luftwaffe was using extended-nose fuses on bombs dropped by Stuka dive-bombers and other aircraft for exactly the same reason. A blast several feet above the ground is many times more effective and has a far greater radius than one that is delayed until the bomb is below the surface.)
The primary U.S. GP bombs are the Mark 80 series. This class of weapons uses a shape known as Aero 1A, designed by Ed Heinemann of Douglas Aircraft as the result of studies in 1946. It has a length-to-diameter ratio of about 8:1, and results in minimal drag for the carrier aircraft. The Mark 80 series was not used in combat until the Vietnam War, but has since replaced most earlier GP weapons. It includes four basic weapon types:
Included in the floor display is a submarine fired torpedo. Closer examination will reveal that the torpedo on display is of the practice type. These were normally the same size and weight of the real deal, but did not contain an explosive. Yes, even in the Navy, practice does make perfect!
Generally, this mine type is set to float just below the surface of the water or as deep as 16 feet. A steel cable connecting the mine to an anchor on the seabed prevents it from drifting away. The explosive and detonating mechanism is contained in a buoyant metal or plastic shell. The depth below the surface at which the mine floats can be set so that only deep draft vessels such as aircraft carriers, battleships or large cargo ships are at risk, saving the mine from being used on a less valuable target. In littoral waters it is important to ensure that the mine does not become visible when the sea level falls at low tide, so the cable length is adjusted to take account of tides. Even during the Second World War, there were mines that could be moored in 300 meter (just under 1,000 feet) deep water (such as the Mark 6 sea mine) shown on display at Estrella Warbirds Museum.