Station HYPO

Radio intelligence (RI) gave Admiral William “Bull” Halsey, Commander Task Force 16.1 aboard the USS Enterprise (CV 6) indications and warning to lunch 16 B-25 bombers from USS Hornet (CV 8) 750 miles from Tokyo on April 18, 1942.

Known as the Doolittle Raid, this was the first U.S. air raid to strike the Japanese home islands during WWII.  Below is the after action report from the RI unit onboard USS Enterprise TAD from Wahiawa Hawaii.

DOOLITTLE RAID
U.S.S. ENTERPRISE INTERCEPT UNIT
APRIL 1942

Intercept Unit Roster:
Lt. Slonim – Language Officer
Howard Cain RM1C Intercept Operator
Willie Wesper RM1C Intercept Operator
Roy Lehman RM1C Intercept Operator
Ray Rundle RM2C Intercept Operator

The exact date this unit reported aboard ship is not recalled. All members, except Lt. Slonim, were based at Wahiawa; all volunteered for the assignment without knowledge of the task force objective.

The unit was provided with some frequency and call sign identification information but it carried no radio receivers or other principal equipment except for RIP-5s.

On reporting aboard ship the members of the unit were assigned berthing spaces and then reported to the main transmitter room where Chief Warrant Officer Abernathy briefed us on the use of the receivers and antennas we would be using for intercept. We were not assigned a separate space. We were simply crowded into the transmitter room as extra cargo and the ship’s crew had to work around us. Security was compromised insofar as the transmitter room crew was concerned but they had been briefed as to requirements for secrecy. The transmitter room, itself was declared off limits to everyone except those who possessed proper security clearance. (As far as I know, the security clearance procedure had not yet been initiated). Admiral Halsey could have visited the space but didn’t. At one point during the cruise the ship’s First Lieutenant attempted to enter the space but was denied access.

The ship put to sea from Pearl Harbor escorted by destroyers and cruisers (ships’ names cannot be recalled with accuracy) and set a course west by northwest. At this point, the intercept unit still did not know the taskforce objective. After a short time at sea, however, Lt. Slonim briefed the members of the intercept unit and detailed the radio intercept coverage desired. The intercept watch was set immediately since all areas were considered unfriendly at that time. A search position was set up and a continuous watch maintained on the Tokyo fleet broadcast.

After a few more hours of steaming we became aware that we had joined forces with the U.S.S. Hornet and her escorts. As best I can recall the combined taskforce then consisted of two aircraft carriers, four cruisers, eight destroyers and possibly a tanker.  Later this force would be the Shangra La that President Roosevelt referred to after the Doolittle strike. The Hornet presented a peculiar sight indeed with 16 16-25 bombers lined up on her flight deck. The air department on the Enterprise was heavily beefed up with additional fighter aircraft (F4F Wildcats), no doubt in anticipation of enemy retaliatory attacks.

The taskforce maintained a steady course toward Tokyo into increasingly deteriorating weather. The aircraft carriers were taking green water over the bow and the destroyers were taking a terrific beating. The intercept unit intensified efforts to monitor the high frequency spectrum and were soon rewarded by the intercept of units on the enemy picket boat frequencies. At about this time, unfortunately, the enemy chose to implement a massive call-sign change, an event which greatly hampered our efforts to identify individual ship and shore units. The intercept unit did effect some call-sign recovery however by monitoring known shore station frequencies and noting call signs thereon used by well-known shore stations (i.e. Truk, Tokyo, etc.) On the night of the call sign change I intercepted some plain language transmissions between the picket boats which indicated they had not received the new call signs. The control station then proceeded to advise the individual units as to their new call signs. This helped to recover some of the pinko.t boat identities.

At this point, it should be mentioned that the Enterprise was equipped with one of the earlier radar installations and it seemed to be operating satisfactorily according to Chief Warrant Officer Abernathy.

The picket boat frequently reception improved greatly as the taskforce proceeded toward Tokyo and the intercept unit was receiving most, if not all, the traffic originated by these “boats.” This information was relayed by Lt. Slonim to Admiral Halsey of course; CWO Abernathy was also aware of the situation and used the opportunity to alert the radar operators.

During the night hours of April 16th or early morning hours of April 17th the radar picked up surface ships many miles distant. These were assumed to be enemy units of the picket boat force and the Fleet Commander initiated evasive action in an effort to avoid detection. There was great concern here as to whether the task force had been sighted by the enemy and, if so, that the mission would have to be aborted. The intercept unit closely monitored the picket boat frequencies to determine if enemy sighting reports had been transmitted but detected none. This was a major contribution the intercept unit to the fleet commander who then decided, based on this and other information, to resume course toward the objective.

Bad luck lay ahead however. On the morning of April 18th, approximately 8:00 A.M., the taskforce encountered several picket boats head on. For reasons unknown, the radar had not detected the enemy; further, the intercept unit had detected no reports of sightings originated by the picket boats. It was theorized that the picket boats were just as surprised as we were. The taskforce neither slowed nor changed course. Admiral Halsey directed the cruisers and destroyers to break formation, sink all picket boats and then resume steaming position. The intercept unit placed all members on watch, monitoring as many frequencies as possible. The U.S.S. Savannah blew the largest picket boat out of the water with a full turret salvo. We believe it was this boat from which five enemy crewmen were rescued after the boat sank. (Lt. Slonim interrogated these prisoners later but stated he obtained very little useful information). Other taskforce units dropped back on a search and destroy mission, sinking all other picket boats. We could hear the firing in the distance. The Enterprise also launched aircraft to locate and destroy the picket boat force we had eluded a few hours earlier.

The big question posed to the intercept unit was: did any of the picket boats successfully transmit a sighting report to the enemy command. Intercept operators soon confirmed that sighting reports had indeed been transmitted. These were plain language sighting reports which the enemy apparently did not have time to encode. The sighting reports were also detected being relayed on several frequencies which seemed to confirm that they had been entered into the enemy military communications system. Unfortunately, due to the earlier call sign change, we could not specifically identify the levels of command at which the reports had been received.

Again this was a major contribution by the intercept unit because Admiral Halsey had a tough decision to make. Lt. Slonim questioned each intercept operator individually, asking if, in our opinion, a sighting report had been successfully transmitted and received by enemy shore stations. All operators agreed that a sighting report had been transmitted and their opinion was backed up by copies of the intercepts as they were relayed on various frequencies.

It is not known what Lt. Slonim told Admiral Halsey but preparations to launch the B-25s were commenced immediately. The seas were very rough but 16 B-25s successfully took off from the U.S.S. Hornet and set course for Tokyo approximately 800 miles distant. The U.S.S. Enterprise increased the air CAP over the taskforce, reversed course and increased speed. The destroyers had been left behind the day before due to rough seas and the taskforce needed to reform.

The intercept unit work was just beginning. We now had to monitor for enemy ships, and planes. in our area and enemy main island frequencies for air, ship and submarine as well as attempt to intercept information relating to the attack, or fate, of the B-25s. We continued to note moderate increased activity on enemy frequencies, possibly caused by the sighting reports but this did not seem to result in increased levels of encoded traffic on major command frequencies. These circumstances prevailed until the B-25s arrived in their target areas. The first indication of their arrival was intercepted on the Tokyo Fleet Broadcast, the familiar HI HI HI repeated over and over many times. This information was relayed immediately to Admiral Halsey. Thereafter we intercepted many plain language messages and many of them correctly identified the attacking aircraft asB-25s. Lt. Slonim interpreted the contents of all plain language messages for Admiral Halsey. One intercept message identified a B-25 heading on a course to Vladivostok. It was subsequently learned that one B-23 had indeed landed at Vladivostok.

Much later we learned that the crew had been returned to the U.S. but not the aircraft.

The intercept unit remained on the Alert with all operators on watch in order to cover as many frequencies as possible. Some hours later we were further motivated by a report that a Kawanishi flying boat had overflown the taskforce. Apparently the aircraft did not sight the taskforce, due to heavy cloud cover; whatever the circumstances no sighting report was intercepted. Again, Admiral Halsey relied on the intercept unit because the decision was made not to direct fighter aircraft to the flying boat for fear of revealing the taskforce position. This was essentially the last contribution by the intercept unit but it continued to maintain watch while steaming back to Pearl Harbor.  All intercept operators disembarked at Pearl and returned to Wahiawa.

It should be mentioned parenthetically that the intercept unit received outstanding support from Chief Warrant Officer Abernathy and his transmitter crew. Accommodation of the intercept unit in their space was a great inconvenience but all hands accepted the very trying conditions in good spirit. The U.S.S. Enterprise was a “happy” ship and I felt fortunate indeed to be a part of it on this operation.

One final note. Each member of the intercept unit received the Presidential Unit Citation based on our service aboard the U.S.S. Enterprise during this operation as did each and every crew member on that ship.

The Doolittle Crew