25 February 2012

The Grumman A-6E TRAM: Making the Intruder More Lethal

The patch worn by A-6 Intruder crews. Note the radar and TRAM sensor symbolism
The main variant of the Grumman A-6 Intruder to fight in the Vietnam War was the first production version, the A-6A. The next two variants, the defense-suppression A-6B and the night attack-optimized A-6C, were just modifications of the basic A-6A variant and both the B and C versions served in only small numbers given their specialized roles. The next variant was actually the tanker version, the KA-6D. With the experience of combat, the Navy went ahead with the A-6E variant in 1968 which improved upon the deficiencies of the A-6A and replaced many of the 1950s-era systems with more modern equipment. With combat experience in the skies of Southeast Asia and over ten years of technological advancements, the A-6E was a major upgrade in capability, reliability and maintainability over the A-6A, with newer engines, a digital nav/attack system, a single multi-mode radar (the A-6A had two radars, which is why the Intruder had such a portly nose), and built-in test equipment that allowed the bombardier/navigator (B/N) to test the avionics before takeoff. On 22 September 1972, VA-85 "Black Falcons" embarked aboard the USS Forrestal were the first unit to take the new A-6E on an operational cruise. 

However, the navigation system of the new A-6E proved to be a weak spot and a few short years after the A-6E deployed with the fleet, CAINS (Carrier Airborne Inertial Navigation System) was added to the Intruder. Using the Litton AN/ASN-92 which was the same INS system used on the Grumman F-14 Tomcat and Lockheed S-3 Viking, an Intruder B/N literally plugged the aircraft's INS into the aircraft carrier's navigation systems to get a quick and very accurate initial fix before departing on a mission. But the most dramatic improvement to the capabilities of the Intruder came about at the same time as CAINS. At the time, there were a number of Intruder combat veterans assigned to the Office of the Chief of Naval Operations (OpNav) and with the Naval Air Systems Command. They spent their time getting upgrades and improvements pushed out to the Intruder fleet like CAINS.

A-6C TRIM. Note the prominent ventral gondola for the sensor.
One of the officers, Lieutenant Commander Lyle Bull, was working in the Aircraft Requirements Directorate of OpNav and decided to see what he could do to make the Intruder a full-capability all-weather/night attack aircraft that they had always dreamed about in Vietnam. During the war twelve A-6As were converted into the A-6C which had a large ventral gondola that housed the TRIM (Trails/Roads Interdiction Multi-Sensor) unit that had a FLIR and low-light TV (LLTV) unit for night attack missions over the Ho Chi Minh Trail. Large and aerodynamically bulky, TRIM also suffered from the relatively primitive state of the art in sensor technology at the time. Bull decided that TRIM was a good starting point for an improved system for the A-6E. This improved system became TRAM- Target Recognition Attack Multi-Sensor. In his position with OpNav, Bull had seen the state of the art in infrared technology and made the astute observation that there was space in the Intruder for an internal installation- because, as he put it, "Pods and sailors are not compatible". In the A-6A there was a separate search radar and a track radar in the portly nose- with the A-6E, a new Norden unit combined the functions into one radar and there was now space where the track radar used to be in the lower portion of the nose section. Bull had figured out that a 400-pound installation would fit perfectly into the space. 

In briefing his superiors on what TRAM could do for the A-6E, he pointed out that unlike TRIM which could only search and identify targets, TRAM would also incorporate an internal laser designator to mark targets for the new generation of laser guided bombs under development. Combined with the advances in sensor technology, an A-6E TRAM had a drastically improved bombing accuracy with miss distances of less than 10 feet, while today routine, such accuracy was stunning in the 1970s. However, in the lean funding environment following Vietnam, money for the R&D for TRAM had to be raided from other Naval Air Systems Command programs. Bull's superior, Rear Admiral Donald Davis, authorized $15 million in initial funding with the warning that the funding came from other programs which mean Bull wouldn't be liked- "They'll be after your ass, so watch yourself", he warned. 

A-6E TRAM prototype. Note the compactness of the installation.
Both Hughes and Texas Instruments agreed to develop competing designs for TRAM and Grumman readily agreed to handle testing and integration. Both systems were broadly similar differing in sensor details. TI had the advantage having developed the TRIM sensor during Vietnam- however, Hughes' design proved to better in testing and it was selected for the TRAM contract. As part of the TRAM integration, Grumman took the opportunity to upgrade the radar so it was better integrated with the TRAM sensor along with a new intertial navigation system. TRAM B/Ns would remark on the ease and simplicity of operating the laser designator. 

The A-6E TRAM prototype made its first flight at Grumman's Calverton facility on Long Island on 22 March 1974. With only a year of systems integration testing, Bull's system proved to be winner and the Navy began to procure TRAM units for the A-6E fleet. The first production A-6E TRAM flew on 29 November 1975 with VA-42 "Green Pawns" at NAS Oceana getting the first examples on 1 December 1975. Combined with CAINS, by the early 1980s the entire A-6E fleet was flying the most lethal Intruder variant yet and by that time, a Direction and Ranging Set (DRS) and Airborne Moving Target Indicator (AMTI) were added to the aircraft. This all made the A-6E TRAM Intruder the most accurate all-weather attack aircraft in the fleet if not all of the US forces. It would culminate with the A-6E TRAM being responsible for 85 percent of all the laser designations and LGB drops during Desert Storm. 

Source: Intruder: The Operational History of Grumman's A-6 by Mark Morgan & Rick Morgan. Schiffer Publishing, 2004, p131-133.

24 February 2012

The 24th Combat Mapping Squadron: Unsung Heroes of the Pacific War

Squadron emblem of the 24th Combat Mapping Squadron
While much has been written about the superiority of the Consolidated B-24 Liberator versus the Boeing B-17 Flying Fortress in the Pacific Theater during the Second World War (in short, it could carry more a longer range and at higher speeds than the B-17), there is one role that the B-24 played in the Pacific that still remains relatively unknown to most, that of combat mapping. The missions flown in particular by the 24th Combat Mapping Squadron in the China-Burma-India theater were of tremendous contribution to the overall war effort even though the crews of the 24th CMS fought their battles with rolls of film rather than bombs. 

On 2 September 1942, the 24th Combat Mapping Squadron was established as the 24th Photo Mapping Squadron at Petersen Field in Colorado Springs, Colorado. They were subsequently moved to Will Rogers Field in Oklahoma City to operate the reconnaissance variant of the Consolidated B-24 Liberator which was designated the F-7. Prior to the creation of an independent United States Air Force, the "F" designator was used for photo reconnaissance aircraft while the "P" (for Pursuit) was used for fighter aircraft. The first F-7s arrived in January 1943 as basic conversions of the B-24D Liberator which removed all bombing equipment and replaced with eleven cameras. All the defensive armament of the Liberator was retained. Most of the conversions to F-7s were done at Lowry Army Air Field in Denver, but additional examples were also converted by Northwest Orient Airlines at their Minneapolis maintenance base. Most of what the 24th did in Oklahoma City was the training of crews to prepare for deployment to the Pacific. Unlike other reconnaissance crews, though, the 24th CMS would be tasked with providing detailed aerial photography of the China-Burma-India area for the creation of detailed navigation maps as well as other types of maps needed for the war effort. 

The unit arrived at Guskhara, India in January 1944 with improved versions of the F-7 which were designated F-7A. The F-7A photo recon Liberator was based on the nose-turret equipped B-24J Liberator. A trimetrogon arrangement of cameras were mounted in the nose (an additional window was fitted in the lower side of the nose for the lateral cameras of the trimetrogon cameras) and a pair of vertical cameras for stereo-photography were fitted in the aft bomb bay (a pair of windows were fitted in the aft bomb bay). The additional windows were the identifying features of the F-7A. The forward bomb bay carried additional fuel tanks while the aft bay was sealed shut to provide a compartment for the camera technicians and environmental systems that kept the cameras and long rolls of film at a constant temperature. Again, like the original F-7 variant, the full defensive armament was retained. 

Developing the photos from a mapping mission.
The first missions to map the CBI area commenced in March 1944 in support of the US Army Air Forces' Tenth and Fourteenth Air Forces- it was the Fourteenth Air Force under General Claire Chennault that replaced the original American Volunteer Group which was also known as the "Flying Tigers". In addition, the 24th CMS also flew missions mapping Burma in support of the British 14th Army. While provisionally based in India, the squadron sent detachments of aircraft to operate from forward bases in China as well as more remote parts of India closer to the Burmese border. At the time, the only heavy bomber group based in China was the 308th Bombardment Group which flew B-24Js. The only logistical route for the support of the war effort in China came via the air route over the Himalayas called "The Hump". Frequently the B-24Js of the 308th BG had to be stripped of armament and fly their own bombs and fuel supplies from India over "Hump" the bases in China. It usually took three "Hump" missions by a single B-24J to transport the bombs and fuel needed for it to fly a single mission from China against Japanese targets all along the Pacific Coast of China, Vietnam, and Malaya. The photo-mapping F-7As of the 24th CMS also flew their own transport missions over the "Hump", with 182 "Hump" crossings made in 1944, often at well above maximum gross takeoff weight. Six F-7As were lost on these transport missions alone in 1944. 

Large areas of China lacked any maps at all, much to the frustration of the 308th BG. Many of the missions to map the interior of China were well over 2,500 miles in length. In addition, detailed mapping flights were made over Malaya (modern-day Malaysia), Vietnam, Thailand, and Burma. During the summer of 1944 the Japanese went on the offensive in central China to eliminate the forward bases of the 308th BG and numerous overflights of territory being contested were made to provide battlefield commanders accurate maps to blunt the Japanese offensive. Detailed maps were also made from overflights of all the Pacific ports of China that were being used by the Japanese to bring supplies to their forces in area. A less hazardous mission involved photo-mapping the entire supply routes from Allied bases in India over the "Hump" to Chinese forward bases. Air Transport Command's pilots benefited from a detailed map that covered a 50-mile wide strip from Calcutta all the way to Kunming in central China. 
24th CMS Consolidated F-7A Liberator. Note the camera windows.

By 1945 the 24th CMS had mapped 455,000 square miles of territory in India, Burma, Thailand, and Malaya. An additional 435,000 square miles of China were also mapped. The greatest challenge in the area for the 24th CMS wasn't Japanese resistance as the F-7As operating singly or in pairs were usually left alone but the weather. An astounding 50% of the missions flown were unsuccessful because of bad weather in the areas to be mapped!

Just prior to the end of the Pacific War the 24th CMS had a forward detachment also based in Clark AB in the Philippines to assist with mapping of that nation as the last of the Japanese resistance was mopped up. Following the Japanese surrender, another detachment was established in Sydney, Australia, to assist the Australians with the mapping of the continent which lasted well into 1946. By that point, the unit was converting to the photo reconnaissance version of the Boeing B-29 Superfortress, the F-13A. The unit returned stateside in late 1947 to Hamilton AFB in California before being disbanded in 1953 at Lake Charles AFB, Louisiana. 

Sources: B-24 Liberator Units of the CBI (Osprey Combat Aircraft No. 87) by Edward M. Young. Osprey Books, 2011, p88-89. Combat WWII Squadrons of the United States Air Force: The Official Military Record of Every Active Squadron, edited by M. Maurer and the USAF Historical Division. Smithmark Publishers, 1992, p126-127. Photos: University of Chicago, Mark Styling (illustrator for the Osprey title).