In early 1945 the Far East Air Forces (FEAF), the air component in the Southwest Pacific Area (SWPA), had a dilemma. Up until this point of the fight, Japanese air defenses had been relatively unsophisticated--mainly visual observers, a few early warning radars, and optically guided anti-aircraft guns. As the Americans moved closer to Japan, the technology associated with air defense dramatically improved. As US forces closed in on the Philippines the density of early warning radars increased, providing Japanese forces with better warning of inbound allied air raids. In December 1944 the first instance of fire control or gun laying radars was recorded outside of Manila near the former Clark Field. These radars helped searchlights find targets at night as well as aided the pomting of anti-aircraft guns when clouds prevented optical tracking of aircraft. FEAFs rapid response to this electronic threat highlights the innovation and organizational flexibility that existed within the SWPA.
During the Second World War, Allied signals intelligence (SIGINT) and electronic attack efforts were both carried under the umbrella of radar countermeasures (RCM), with the former being seen as 'passive' and the latter 'active.' Passive RCM had its start in the Southwest Pacific Area (SWPA) in early 1943. A loosely orchestrated group of British, Australian and New Zealand RCM observers rotated through available assets, including 90th Bomb Group (H) B--24Ds, 403rd and 435th Bomb Squadron B--17s, and RAAF Catalinas and Hudsons. The RCM observers would lug aboard their heavy Hallicrafter S-27 or Australian SN-2 radar intercept receivers and ride along on standard bombing or patrol missions, noting Japanese radar activity and writing up the results in post-mission reports. Soon this activity with USAAF units would be formalized with the 'ad-hoc' ferrets found in many SWPA Heavy Bomb Groups.
'Ad-hoc' ferrets (a contemporary term used by aviation historians) are standard bomber aircraft field-modified with racks, cabling, and antennas that enable them to carry radar receivers and other SIGINT equipment on an a periodic basis, usually as a secondary mission to a primary function of bombing. Shortly after arriving in theater at Fenton Field, Australia in May 1943 the 380th Bomb Group (H) started flying its first 'ad-hoc' ferret missions. Initially, a handful of Group B--24D aircraft were fitted out with racks, cabling and antennas to support radar receivers operated by Royal Air Force, Royal New Zealand Navy, or Royal Australian Air Force (RAAF) RCM observers on loan to the unit. (1) Key to coordinating this effort was Section 22.
Founded in Brisbane, Australia in July 1943, Section 22 reported to the Chief Signal Officer of General Douglas MacArthur's General Headquarters of the Southwest Pacific Area (GHQ SWPA). Originally named "Radio and Radar Countermeasures Division" until November 1943, Section 22 combined all Allied activities--not only US Army Air Forces and US Navy but also British Commonwealth and Dutch personnel--in a coalition effort to understand the Japanese use of radar and develop countermeasures to ensure the success of Allied operations. (2) Geographically separated subordinate elements called "Field Units" provided information to the headquarters through a myriad of reports. Some of the intelligence was actual 'hands-on' exploitation of captured Japanese equipment while other was electronic intelligence--intercepts of Japanese radar signals from air, land or sea-based platforms. (3)
In August 1943 Field Unit 6 was attached to the 380th Bomb Group (H) as a radar countermeasures unit. Composed of a mix of Australian and American airmen, the unit set about installing radar receivers in the 380th's 'ad-hoc' ferret B-24s. The unit followed the 380th Bomb Group (H) around the SWPA, arriving at Mindoro, PI in March 1945 from Darwin. (4) Field Unit 2 supported the 90th Bomb Group (H), likely forming in late 1943, with Field Units 1 and 16 supporting the 43rd and 22nd Bomb Groups appearing in either late 1943 or early 1944.
Ferrets--overview, Fenton Field operations--up through August 1944
MacArthur's planned offensive against Rabaul, a key Japanese base on New Britain, was given approval by the Joint Chiefs of Staff in spring 1943. Executed as Operation CARTWHEEL, the plan required detailed knowledge of Japanese defenses in the region. This action likely galvanized the creation of Section 22 and provided the impetus and priority to move from an ad-hoc approach of radar reconnaissance to a more formal structure with proper equipment. Backed by a Joint Chiefs directive, the staff at GHQ SWPA soon went calling to Washington and at a meeting on July 22, the Army Air Forces agreed to build two ferret aircraft to aid GHQ SWPA in gathering SIGINT for current and proposed operations. (5) In January 1944 the two modified B-24Ds, now identified as Ferrets VII and VIII, arrived in theater. Although administratively assigned to the 63rd Bomb Squadron, 43rd Bomb Group (H) for maintenance, the mission tasking of the ferrets was controlled by Section 22 through Field Unit 1.
Ferrets were bomber aircraft modified to be dedicated SIGINT aircraft, with the bomb bay sealed and additional crew members and equipment carried in the new compartment. The first 28 operational SWPA ferret missions were flown around New Britain, New Ireland, and the north coast of New Guinea. (6) In early April the ferrets moved from Nadzab, New Guinea to Fenton Field, Australia and were temporarily assigned to the 530th Bomb Squadron of the 380th Bomb Group (H). By the end of August the Fenton Field-based ferrets had mapped the Banda Sea and Borneo region and were ready to join the fight for the Philippines. The Allied liberation of Owi Island enabled the ferrets to move northward and rejoin the 63rd Bomb Squadron in early September 1944, arriving in time to survey Morotai and the Palaus before the allied landings. (7)
Between September 24, 1944 and January 7, 1945, Ferrets VII and VIII flew 33 missions throughout the Philippine archipelago, charting the Japanese air defenses of the former US colony. It was realized that only by searching during a strike could it be determined how the Japanese used their radars against enemy aircraft, be it searchlight, gun-laying, or ground controlled intercept by fighter aircraft. For this reason, before 'ad-hoc' ferrets proliferated, Ferrets VII and VIII accompanied several strike missions. (8)
Though their plotting accuracy and ability to characterize a signal was impressive, the Section 22 ferret force was only two aircraft and had a limited reach across the broad SWPA Theater. To help keep track of the changing Japanese radar electronic order of battle, Heavy Bomb Group 'ad-hoc' ferrets were used to help ascertain Japanese radar coverage. This data routed back to Section 22 staff officers who compiled radar coverage charts that aided in mission planning and helped determine bomber routing to minimize USAAF aircraft detection and ensure surprise over the target area, mainly of light and medium bombers. This not only helped against Japanese anti-aircraft fire, it also reduced warning time given to Japanese fighter units and allowed SWPA assets to perform surprise strikes against enemy airfields. (9)
By mid-1944 Section 22 had accumulated a large number of APR-1 receivers and APA-6 pulse analyzers and started to create a force of 'ad-hoc' ferrets for the V Bomber Command. Six 'updated' aircraft were delivered to the 380th Bomb Group (H) to augment and replace their earlier 'ad-hoc' ferret force and an initial delivery of aircraft was made to the 90th Bomb Group (H), enabling both groups to fly at least one 'ad-hoc' ferret equipped with a receiver and pulse analyzer on each strike. By January 1945 all four Heavy Bomb Group in the Fifth Air Force were operating 'ad-hoc' ferrets. (10)
Just as the equipping of the 'ad-hoc' ferret fleet was done on a shoestring, so was the manning. The USAAF RCM Observer Course at the Radar School at Boca Raton, Florida had a limited throughput. Officers who graduated from this course were generally put in leadership positions at the Field Units or on staff with Section 22. The majority of the personnel used to operate the equipment on the SWPA 'ad-hoc' ferret aircraft were enlisted airmen and Allied personnel. RAAF airmen continued to fly with the US Heavy Bomb Groups through May 1945, slowly being augmented then replaced with USAAF radar mechanics. Section 22 set up an RCM School in theater to train enlisted radar mechanics to be flying RCM Operators, with classroom academics and flights in a C-47 augmenting the stateside training they had received. (11)
To China and Beyond
Far East Air Forces--created in June 1944 with the Fifth and Thirteenth Air Forces--were focused on supporting the Army drive through New Guinea to the Philippines. This support came in the form of attacks against Japanese supply and transportation forces as well as counter-air attacks against Japanese air assets. As airfields were seized in the southern Philippines in late 1944, the Heavy Bomb Groups assigned to Fifth Air Force were able to start ranging Japanese transportation and industrial targets in littoral China as well as French Indo-China and Formosa.
Up through 1944, the SWPA RCM program concentrated on the 'passive' side of the house--mapping Japanese radar locations and being on the alert for new signal types. This all changed at the end of the year. Save one or two instances in North Borneo, the only Japanese radars encountered had been those associated with early warning - radars that gave rough range and azimuth to the Japanese to provide warning of an impending raid but not accurate enough to direct searchlights or anti-aircraft fire at night or bad weather. On a strike against Clark Field outside Manila at the end of December 1944 a Japanese 'Gun Laying' (G/L) or anti-aircraft...