The Role Of Interdiction
In military terms, Interdiction is the use of armed force to slow down or stop the flow of supplies and personnel needed by an enemy to continue hostilities. It is one of the most important aspects of modern warfare. If you can dry up an enemy's food and ammunition, he will lose his ability to fight and will eventually be forced to lay down his arms.
During World War II the conflict was spread over the entire globe and the interdiction of Axis supplies took many forms. Strategic interdiction was accomplished through two major means, naval blockade (primarily by submarine), and aerial attack by heavy bombers. Both US and German submarine forces were very successful at interdicting supplies being transported by sea. The aerial interdiction of strategic materials by Allied heavy bomber forces was so complete that by war's end both the German Air Force and the Japanese Air Force were virtually grounded for lack of fuel.
Tactical interdiction was accomplished by fighter bombers and/or light and medium bomber forces. The daylight interdiction of German supplies in the European Theater was accomplished through these means. "Operation Strangle", during 1943, cut off supplies to the German front lines in Italy so effectively that the capture of Cassino and the eventual liberation of Rome were a direct result. Field Marshal Kesselring's troops simply did not have the ammunition and supplies needed to carry out effective defense. Interdiction of the Normandy coastal areas, and a little stupidity on the part of Hitler, kept the Germans from mounting the counteroffensive needed to push the Allies back into the sea. With total air superiority, American P-47s and British Tempest fighter-bombers were able to roam freely over the French road and rail net behind the invasion beaches, bombing and rocketing German supply trains and armored columns bound for Normandy. The end result was, of course, the successful interdiction of the Normandy Invasion beach and an eventual Allied victory in Europe.
In the Pacific the situation was entirely different. Japanese troops and supplies were moved almost exclusively by ship. And while the American submarine forces extracted an enormous toll of Japanese shipping they simply couldn't cover enough area. Allied fighter aircraft were called upon to fill the breach but were not heavily enough armed to do the job. Neither were the standard light and medium bomber aircraft, unless they could get a good bomb hit, and hitting a twisting, turning ship with a bomb is not easy. To solve these problems an idea was born which would eventually lead to the gunship concept. In 1943, Major Paul 1. "Pappy" Gunn (a more fitting name even Hollywood couldn't have thought up) rearmed some of his A-20 Havoc light bombers for the strafer role. Four .50 caliber machine guns were mounted in the nose replacing the bombardier's station. The experiment was a success but the concentrated fire of only four .50s was barely adequate to sink a Japanese merchantman, let alone an armored escort vessel.
"Pappy" Gunn decided to mount much heavier armament on a larger airframe with more powerful engines, the North American B-25D Mitchell medium bomber being chosen for the new role. Again, four .50s were mounted in the nose, an additional pair of .50s were mounted on each side of the fuselage, and a tray package of three more .50s was mounted just aft of the nose wheel bay. When General George Kenney inquired about the center of gravity of the nose heavy machine, "Pappy" quipped "Oh we threw the CG away!" The concentrated firepower of eleven .50 caliber machine guns could literally cut a merchant vessel in half. Gunn's "Commerce Destroyers" really showed their stuff at the Battle of the Bismarck Sea in March 1943 when the gunships, B-25s and A-20s, systematically destroyed an entire Japanese convoy of twelve merchant ships and ten cruisers and destroyers. Ninety thousand tons of shipping and 15,000 Japanese troops were slaughtered. The gunship concept had been proven. Later in the war specialized gunship B-25G, H and J, along with the Douglas A-26B Invader, were mass-produced.
Night interdiction was virtually non-existent during World War II. Effective night interdiction tactics were not developed until the Korean War. Night flying was given more emphasis in pilot schools and radar was rapidly being perfected. In Korea, a device called SHORAN (SHOrt RAnge Navigation radar) was developed for the night combat role. It was a simple idea whereby two radar beams intersected each other over the potential target and the bombers merely 'rode' one of the beams to the intersection and dropped their ordnance. Extremely effective against bridges, rail yards, or truck parks. Stationary targets, moving vehicles, or trains, still had to be hunted down individually.
Night flying Douglas B-26 Invaders (redesignated from A-26) were the aircraft most used for night interdictions in Korea. Fast, long-ranged, B-26s carried eight 50 calibre machine guns in the nose and another six .50s in the wings. Hunter-Killer teams of Invaders were out nearly every night. The Hunter aircraft would fly up and down the Korean countryside looking for headlights or locomotive steam plumes. Passing by the potential target, the Hunter aircraft would then call in the Killer aircraft reporting what he had seen. Often times communist drivers would turn their lights back on at just about the time the Killer aircraft would arrive. Trains were often times bottled up by Hunter aircraft bombing the tracks both in front of and to the rear of the train, thus stuck in place to await destruction by the Killer aircraft or fighter-bombers the next morning. After the Killer aircraft had expended his ordnance the team roles would be reversed. Other tactics and equipment were tried including the use of wing-mounted searchlights on B.26s, but the most effective tactic was still the one plane/one mission raid with all eyes aboard watching for something unusual in the night. These tactics were proven out by the thousands of trucks and hundreds of rail cars and locomotives destroyed by the three B-26 wings in Korea.
The intervention in Vietnam, which later became a full-fledged, though undeclared war, brought new problems of night interdiction. First off, the US Air Force had no active aircraft suitable for the night interdiction role. The closest thing available was the Martin B-57 Canberra twinjet bomber. But it suffered from three major deficiencies; it was too fast for night interdiction; being a jet it drank fuel at an enormous rate and consequently had a very short loiter time; and lastly, its armament was too light for the job.
The answer was in the Air National Guard and Air Force Reserve aircraft pool, and in the Arizona desert-the Douglas A-26 Invader. The South Vietnamese forces needed close air support immediately and the only aircraft available, since VNAF crews were not jet-trained, were the venerable old Invaders left over from two previous wars. With its great loiter time and ordnance load, it was ideal for close support missions and interdiction attacks against the flow of traffic down the Ho Chi Minh Trail, which brought supplies to the Viet Cong. Unfortunately structural problems arose which caused a major rebuilding of all the combat airframes resulting in an almost entirely new aircraft....the B-26K, rolled out of the On-Mark Engineering facility in Van Nuys, California in 1964. The new B-26K (Air Force designation A-26A) was assigned to the 609th Special Operations Squadron at Nakhon Phanom AB in Thailand, a short hop from The Trail. The job of the 609th was truck-busting along The Trail. As in Korea, the Invaders proved to be exceptional at this role. But so were the North Vietnamese at hiding from the prying eyes of the Invader pilots.
more sophisticated aircraft was needed. The B-26K was finally phased out
of combat in late 1969. They were replaced with the most effective night
interdiction and support weapon yet seen...the side-firing gunship.
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