Depth Charges

Depth Charges
*"A depth charge has a magnificent laxative effect on a submariner."* *Lt. Sheldon H. Kinney, Commander, USS Bronstein (DE 189)*

HISTORY At the start of WWII, the USN had no adequate depth charge and adopted the British designed Mark 6 and fitted an American-designed hydrostatic fuze. During WW2, the USN concentrated on increasing the depth at which a submarine could be attacked and made design modifications to increase the sink rate of depth charges. A successful depth charge attack had to be extremely accurate to destroy a German submarine. The hydraulic "water hammer" effect created by a 300-pound depth charge would destroy the submarine if detonated within 10 yards of the hull, 30 yards away only damaged the hull. Later in the war the magnetic impulse detonator (Mark 8) was introduced, which triggered the depth charge when it was in close proximity to a submarine. American Destroyer Escorts carried about 100 depth charges on board. In 1943 the Mark 9 was introduced. Designed to sink fast and detonate at up to 1000 feet, the MK 9/14 was aerodynamically shaped, lead-weighted and finned. Although the explosive payload was reduced to only 200 pounds, the greater hull pressures at extreme depths rendered the submarines more fragile, thus reducing the need for large explosive payloads. The British chose the opposite path, equipping their DEs (actually Captain-class frigates) with two 3,000 pound Mark X depth charges in December 1944. The unique Mk X depth charges contained 2,000 pounds of explosive and were intended to combat the newest deep-diving German submarines. The use of rear drop racks was a useful strategy in WWI, but by WW2 submarine technology and acoustic sensors had progressed significantly. U-boats were was able to detect engine and cavitation noises of pursuer's propellers and the splashing of their depth charges. The early Mk 6 depth charges took between 50 and 75 seconds to sink to 600 feet (the maximum U-boat depth). The newer Mk 9/14 depth charges were designed to sink faster but still took between 26 and 41 seconds to sink the same depth. This lag time allowed the U-boat captain to navigate away from the danger area. During WW 2 Captain Johnnie Walker, RN developed a technique called "creeping". Recognizing electric powered DEs were much quieter than diesel-powered boats, especially when running below 6 knots when the propeller cavitation noises were greatly reduced, the DEs teamed up to kill U-boats. The "pusher" DE would churn around making noise and actively searching with sonar. A second DE would "creep" along quietly without sonar, receiving direction and depth instructions from the "pusher". When the creeper was properly positioned, it would drop depth charges, hoping the U-boat was paying more attention to the "pushers" position and noise. If the U-boat detected the splashing noises of the "creeper's" depth charges, he would assume they belonged to the "pusher" located several hundred yards away and representing no threat. The British used the creeper technique with great success with the lend-lease DEs, which they called "Captain's class Frigates". The United States abandoned depth charges after World War II, preferring torpedoes and ahead thrown proximity contact weapons.
Nomenclature: Mark 6 (depth fuze) and Mark 8 (magnetic influence) "Ashcan" Weight: 345 pounds Charge: 300 pounds of TNT Sinking Speed: 8 - 12 feet/second. Depth: 30 - 300 feet These were an older depth charge that was cylindrical in shape, about 28 inches long and 18 inches in diameter. They contained 300 pounds of TNT. These were primarily used in the Mark 9 roller racks but could also be fired from the Mark 6 K-Guns. These early style depth charges had a tendency to tumble unpredictably in the water, which led to irregularly shaped depth charge patterns. Later, the Mark 9 and 14 "fast sinkers" were developed to counter this lack of predictability. Mk 6 Depth charges being loaded aboard the USS Roper (DD-147), an old Wickes-class flush-deck destroyer. The Roper was commissioned on 19 March 1918. She sank *U-85* off Cape Hatteras on 14 April 1942. She would be scrapped in 1946 after 38 years of service.
Nomenclature: Mark 7 (depth fuze) "Ashcan" Weight: 645 pounds Charge: 600 pounds of TNT Sinking Speed: 8 - 12 feet/second. Depth: 30 - 300 feet The Mark 7 was cylindrical measuring 28 inches long and a diameter of 25 inches. It was launched from the Mark 9 roller racks but not the Mark 6 K-Guns.	No photo available.
Mark 9 (depth fuze) and Mark 14 (magnetic influence) "Fast sinkers": These were the later type of depth charges and had an aerodynamic shape, and a lead-weighted nose to increase their sink rate. Weight: Approximately 450 pounds Charge: 200 pounds of Torpex or HBX Sinking Speed: 14.5 - 22.7 feet/second. Depth: 30 - 1000 feet. The Mark 14 could explode at any depth. The Mark 9 and Mark 14 was a teardrop-shaped, fast sinking weapon. It had fins that spun it for stabilization while it sank and also produced a more reliable sink rate resulting in predictable depth charge patterns. Both depth charges were identical in appearance measuring 28 inches long and 18 inches in diameter. They could both be launched from either the Mark 9 roller racks or fired from the Mark 6 K-Guns.	K-guns firing. National Archives #26G7144211 K-gun firing at night. National Archives #26G1553
On the right is a close-up of the nose-fuze of the Depth fuze, Mark 9, Mod 4 on display at the USS Bowfin Submarine museum in Honolulu, Hawaii. The outer ring is clearly marked "Safe" on the left and is marked from 30-300 feet. The small inner ring is marked 300-1000 feet. This fuze was in the stockpile for some time as there are several inspection/rebuild marks stamped on the outer flange. The earliest is 1-52 and the latest appears to be 1-70.