A great example how radio intelligence provided I&W ISO OPERATION “GALVANIC,” during the occupation of the Gilbert Islands, November 6, 1943 – December 12, 1943.

The three Japanese language officers listed below deployed during OPERATION GALVANIC:

  • LCDR Gilven M. Slonim deployed on the USS Indianapolis (COMCENTPACFOR).  He received his language training in Japan 1939-1941 and retired in 1965 as a Captain.
  • LTjg Charles A. Sims deployed on the USS Yorktown (COMTASKFOR 50).  He received his language training at Berkeley/Boulder Class 1942.
  • LTjg William W. Burd deployed on the USS Enterprise and later on the USS Essex (COMTASKGROUP 50.2).  He received his language training at Berkeley/Boulder Class 1942.


The Gilbert Islands, a group of 16 atolls near the equator, were viewed by the U.S. as a stepping stone to the Marshalls and became the first target of the Central Pacific Campaign. In November 1943, the U.S. launched an offensive code-named Operation Galvanic, in which the prime target was the tiny island of Betio in the Tarawa Atoll in the Gilbert Islands. (As part of Operation Galvanic, the U.S. would also send a smaller force to the Gilberts’ Makin Atoll, some 100 miles north of Tarawa. Compared with the taking of Tarawa, the U.S. faced far less Japanese resistance at Makin and the Americans secured the atoll by November 23, 1943.) In late December 1941, Tarawa, a coral atoll located some 2,500 miles southwest of Hawaii, had been seized by the Japanese, who heavily fortified Betio, Tarawa’s largest island.

USS Enterprise (CV 6) during Operation Galvanic, 22 November 1943. (U.S. Navy)

By November 19, 1943, American warships had arrived near Tarawa. Naval and air bombardments were planned for the next morning with the goal of weakening Japan’s defenses and clearing the way for 18,000 U.S. Marines to seize the island. However, the taking of Tarawa would prove to be more difficult than the Americans had anticipated.

Mobile Radio Intelligence Support (verbatim):

“The occupation of the GILBERTS involved for the first time the continued operations of mobile radio intelligence units for a sustained period of time, and was the first time more than one unit (or on special occasions, two units) accompanied the Fleet.  The operation involved landings on MAKIN, TARAWA, and several smaller islands, the support of these landings and the interdiction of Japanese air attacks from the MARSHALLS.  The task groups normally operated separately, so that a single unit could not serve the entire force as had previously been possible.

The approach to the objective was uneventful.  The Japanese in both the GILBERTS and the MARSHALLS were being subjected to continued air attacks by army aircraft from the ELLICE Islands and the general confusion was great.  Shifts of air strength were made continually and Japanese aircraft were kept out of the GILBERTS except when a counter attack against the ELLICE ISLANDS was scheduled.  There were no Japanese search plans noted which approached our force during the run-in.  The first strikes by the carrier force came on November 19.  They were on the islands of NAURU and TARAWA and the reaction was immediate.  A minimum of sixteen planes from ROI NAMUR were staged through TAROA and MILLE, and throughout the day the task groups were constantly being spotted and an attack was carried out on TG 54.4.  This was the beginning of a very confusing period, since there were so many groups of U.S. ships in a small area that it was often difficult to tell which group had been locate when a Jap plane reported a sighting.


The landings went on as scheduled and the task groups alternated in attempting to interdict air opposition by the Japs staged through the southern MARSHALLS.  To do this the task group cruised just south of MILLE, where it bore the full brunt of the Jap attack.  Fortunately the frequencies in this area were well known and it was comparatively easy to predict attacks by watching requests for aviation weather from one island to another.  The tactical frequencies were stable and almost all attacks were carried out on 6115 kcs (1).  The greatest problem at this period was the lack of good call identifications and conversions. ROI NAMUR was the control point for almost all attacks during this period.  On the evening of November 21 the USS Independence was hit.  No attack message was seen to be originated by the Japanese although that tasks group had undoubtedly been spotted during the day.  There was no radio intelligence unit with this group.

Throughout the period that our carrier force stayed in this area, the Japs sent out large numbers of search planes which kept touch with most of the carrier groups during the daylight hours.  Sometimes during the day, and almost always at night, they sent out large, well-coordinated attacks, usually of torpedo bombers.  According to one carrier admiral, these were the best attacks, tactically, ever made by the Japanese.  Fortunately for our forces, the Japanese almost always used plain language tactical signals in order to get their aircraft in position to attack, and when ready they would send the conventional “all units attack” signal.  The information which the radio intelligence units were thus able to give the task group commander was a great help to him in maneuvering the force to avoid these attacks.  A rather spectacular example of the aid these units offered occurred when a group of enemy planes flew directly over one of the task groups at an altitude of not over five hundred feet, on one pitch black night.  The RI Unit had been in contact with these planes; and as the Nips approached and passed over the group, RI continually informed the task group commander that they not only were not attacking but did not even know the ships were below them. The Admiral therefore did not release the guns and the task group was undoubtedly saved from an attack which would certainly have followed any disclosure of our position (2).


As soon as the fighter field on TARAWA became usable our forces began to withdraw from the area, part of them with the intention of making a strike against ROI NAMUR and KWAJALEIN where most of the planes the Japanese were using to attack our forces in the GILBERTS were based.  Two of the radio intelligence units accompanied this force, one being transferred at sea from TG 50.2 to TG 50.3 on November 29, thus giving both the task group commander and the task force commander, who was with TG 50.3, a unit.  This force circled the easternmost islands of the MARSHALLS well out of air search range, and started the run-in from about five hundred miles northeast of KWAJALEIN ATOLL.  There were no indications of Japanese fleet strength at KWAJALEIN as for as could be seen from the local circuits, although one reason for the attack was a previous report that combatant ships were in the lagoon at KWAJALEIN. Almost miraculously the force escaped detection on the run-in, undoubtedly because all available Japanese planes were being used to hit the now U.S. occupied GILBERTS.  It was necessary to pass several islands almost within radar range and under other conditions search planes would certainly have been covering the area.

On Dog Day, December 5, the first alarm came when KWAJALEIN reported, “50 small planes overhead,” thus indicating a complete surprise had been achieved.  During the remainder of the day the force was snooped and located continuously by planes working ROI NAMUR, but probably out of WOTJE ATOLL.  Some of these were shot down but no real attack was launched by the Japs until the evening when once more they tried out their night torpedo plan tactics as the force withdrew from the MARSHALLS.

Unfortunately the attack against ROI NAMUR had not knocked out many of the planes based there (as photo intelligence later showed) and the attack developed that evening was quite impressive.  It began at dusk and continued until long after midnight.  At one time it was estimated that there were forty planes on the radar screen at one time, all of which were torpedo planes.  As before, a considerable amount of abbreviated plain language signaling took place which was again very useful in determining at what moment the task group should turn away from the attack.  Japs were successful in getting one torpedo into the USS Lexington, which did little damage, but were finally either shot down or had to return to WOTJE ATOLL when their gas ran low.  The next day the task group was out of range and well on its way back to Pearl.”

CDR Gilven Slonim, USN RI Officer, and Brigadier General William E. Riley, USMC, Assistant Chief of Staff, Third Fleet


ENS Charles A Sims Assigned as the RI Officer USS Essex 1943

(1) 6115KHz (high frequency)
(2) Great example of Indications and Warnings ((&W) by RI units

Source: Command Display, Corry Station