Japanese Radar, 1943-1944 II

World War II Photograph

The Invasions of Islands

A consequence of the Doolittle Raid on Tokyo was a residue of doubt in the Japanese Command as to the origin of the attack. Aircraft carriers were certainly considered as the most likely base, but because the planes were the normally land-based B-25s the thought remained that they might have come from the Aleutians. The desire to remove such a threat affected the planning of the June 1942 offensive against Midway by supporting the idea of sending a diverting force against these islands. Two carriers were sent to attack the known garrison and airfield at Dutch Harbor while troops were to be landed on the western-most islands of Attu and Kiska. The two carriers accomplished little and were sorely missed at Midway.

The attack on Dutch Harbor did not catch the defenders by surprise, as they had been alerted by intelligence from Nimitz and a timely warning by the SC radar of a seaplane tender. The attacking planes from the Ryujo met lively AA fire, which distracted them enough from their work to keep the bomb damage minor, if smokey. Planes from the Junyo were unable to find Dutch Harbor, hardly surprising given the weather conditions. It was, in fact, remarkable and showed excellent skill that all but one of the aircraft launched were able to return to their ships, the one having been shot down by the waist gunner of a PBY.

Kiska became the first enemy radar to be accurately mapped by a fledgling electronic countermeasures unit. A B-24 equipped with an SCR-587 intercept receiver flew three Ferret missions around the two western-most islands of the Aleutians in early March 1943 and returned with the knowledge that Kiska had two radar sets but Attu none. They produced an excellent contour map of signal strength that showed the most favorable directions of approach. Their efforts were followed by attempts to destroy the stations, but the Japanese were able to repair the damage relatively quickly. Determining the radar potentials of island bases became a standard component of military intelligence for the remainder of the war, generally using cast-off aircraft but with growing importance and support.

So began a three-way war between the United States, Japan and the weather, with the weather the most vicious and dangerous. It was a campaign greatly assisted for the Americans through the rapid equipping of PBY flying boats with ASV mark II, and it was from them that Admiral Charles McMorris learned on 26 March 1943 that a large, well escorted convoy led by Admiral Boshiro Hosogaya was making a major attempt to break the blockade imposed on Attu and Kiska. Action, called the Battle of Komadorskis, opened at 20 km with accurate early salvos of the Americans as a result of radar fire control. In the long-range gun battle that ran for nearly four hours the out-numbered American squadron ended badly damaged with the heaviest unit dead in the water but concealed by smoke. Hosogaya, who had hurts of his own, was unaware of his superior position, broke off the action and ordered the convoy back.

The Pacific War was to have many landings by Allied troops on the beaches of defended islands. The first of these was the invasion of Attu, begun on 11 May 1943 by the 7th Infantry Division, fresh from tropical training that was intended to throw spies off the trail. Whether freedom from spying served these men better than preparation for the conditions they were to encounter does not seem to have been evaluated. The Japanese and the weather provided the invaders ample resistance during an ugly, 18 day fight that showed what things would be like on such places as Iwo Jima.

After the Battle of Komandorskis and the loss of Attu the Japanese decided to evacuate the 1200-man garrison on Kiska. This was accomplished on 28 July by 19 vessels under Admiral Masatomi Kimura that evaded the American blockade, piloted themselves into the harbor, loaded all personnel and departed just as quietly. It was a brilliant performance followed by an elaborately planned and executed American invasion on 11 August that found nothing but a couple of dogs. Despite PBYs with ASV and patrol ships, the evacuation had evaded interception. The key technical element for the Japanese, used both for navigating through fog and evading the blockaders, was the 10 cm mark 2 model 2 radar.

Associated with the evacuation of the Japanese garrison was a strange radar naval engagement the Battle of the Pips. On 22 July 1943 a PBY reported radar contact with seven vessels, and an American group including two battleships and five cruisers headed for the reported position on a wide front. At 0043 hours on 26 July the Mississippi picked up three or four large contacts on the SG at 30 km. This was followed shortly by the FC fire-direction radar reporting five or six. The contacts looked similar to those returned by cruisers or destroyers but were intermittent and unsteady, which was reported to the bridge. At about the same time other vessels reported similar radar sightings. Fire was opened shortly after 0100 at a range of about 23 km by those vessels capable of firing under radar control. It became increasingly clear to the radar crew of the Mississippi that something was seriously amiss. As they had narrowed range the SG contacts retained the same amplitude instead of strengthening, but, much more serious, the echoes of the projectiles and the splashes were stronger than those of the presumed targets. Fire ceased after 25 minutes when it became clear there was no enemy there. When visual observation cleared, moonlight and star shells disclosed no targets. Examination of the ocean surface after daylight found no wreckage, no oil slicks, no survivors nothing but clean ocean surface.

This embarrassing action was caused by anomalous propagation to ranges such that the blips on the scope had returned a few sweeps after the original. They had encountered this phenomenon frequently with the 40 cm of the FC but never with the 10 cm of the SG. The Radar Officer of the Mississippi later reconciled the contact bearings as echoes from Kiska Volcano and the islands of Segula, Little Sitkin and Semisopochnoi. Had the SG and FC sets had a switch to alter the pulse repetition rate as did the CXAM and the SK, the Battle of the Pips would not have taken place. Pulses from targets within the first sweep are unaffected by such a change, but those returning from targets beyond jump on the display as soon as the switch is pressed.

Observing critically the Attu and Kiska landings was Marine Lieutenant General Holland Smith, who was to become the master of amphibious warfare. With army, marine, naval and air forces he would develop this technique to its ultimate. The Gilbert Islands were to be his first test.

Two strategic directions had evolved by late 1943. MacArthur was to clear the Solomons and parts of the Bismarck Archipelago in order to move across the northern part of New Guinea through the Halmaheras to the Philippines. Nimitz was to drive through the rings of island bases to join with MacArthur for the final drive at a location to be decided. In the original expansion Japan had garrisoned many locations throughout the Pacific and was confident that each would demand a dear price for each insignificant atoll. But once these bases lost their aircraft and could receive no resupply, they became prison camps administered by Japan. It then became clear that only those that afforded harbor and air fields for the next step across the Pacific’s continental-sized distances need be taken.

The invasion of the Gilberts took place in late November 1943 as the first step in Nimitz’s plan. The two islands of Tarawa and Makin received a heavy pummeling by bombers and ships’ artillery, but the effect seemed to have hardened rather than softened the resistance of the garrisons. The attackers made no small number of blunders, and Tarawa became inscribed as a Marine Corps memory of courage and blood. The Marshall Islands were taken in early 1944 in a more workmanlike manner. The Marianas were to be next, and it was assumed and hoped that attack on them would precipitate a major fleet action.

While this was going on MacArthur secured the northern coast of New Guinea with troops of the US, Australia and New Zealand. His path was eased by much of the enemy’s naval and air forces that might have faced him having been diverted to help check Nimitz’s drive from the east.

The FC and FD fire-control radars were of little use in identifying land targets for the increasingly important artillery function of bombardment preparatory to landing. Saturation bombing and rocket attacks were spectacular and could be demoralizing, but the need was for accurate fire on targets known to present danger. Such targets could often be identified from aerial photographs but not recognized from the ship either visually or electronically. A solution presented itself as forces began moving up the Solomons in 1943. Prominent land features could be identified on the aerial photographs and seen by radar. This allowed offsets to be calculated so that fire could be directed on dangerous emplacements. The method worked optically too, but accurate ranging made radar preferable even on clear days. It worked even better when the 10 cm mark 8 fire-control radar became available Wherever a landing was made the Australian LW/AW was on the beach soon, augmented in early 1944 by the light-weight SCR-602. They were particularly valued in the New Guinea theater where control of the air was more hotly disputed than in the Central Pacific. Once the islands were secured, local air defense relied on a combination of the SCR-270 and SCR-268; the SCR-602 was considered expendable, but the LW/AW often served when the heavy 270s and 268s could not be got into position. The defenders liked the long range of the 3 m 270 for warning and found the resolution and height data of the 1.5 m 268 good for fighter direction. Australian Mobile Fighter Control Units and American Signals Warning Battalions provided fighter direction whenever it was needed. They naturally assumed a function that endeared them to all Allied airmen guiding lost fliers home and locating downed aircraft. The number saved is not on record, but it is very large.

The SCR-268 may have had its most successful day in directing the 90 mm guns of the 9th Marine Defense Battalion in defending the Rendova (New Georgia) landings in July 1943. Of 16 attacking bombers gun-fire downed 12 with an expenditure of only 88 rounds, leaving the four that escaped to be destroyed by fighters. The island locations were ideal for meter-wave equipment, and crews became so proficient in their use that, unlike their comrades in Europe, who seldom had an excellent sea surface to form consistent vertical lobe patterns, they greeted the arrival of microwaves with indifference and relied on meter waves till the end.

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