The Japanese Seizure of Guam


By Thomas Wilds - Originally Published July 1955

The Japanese plan dictated the most difficult routes. But the Hayashi Detachment got lost, and found an easier way

When Guam fell to Japan on 10 December 1941 it became the first American soil formally surrendered to an enemy in WWII. This was not surprising, for the island had a small garrison, no fixed defenses and was surrounded by strong Japanese bases in the Mandated Islands. In spite of Guam's weakness, the Japanese feared to leave an enemy base in their rear and decided to invade the island at the very beginning of the war. This is the story of the seizure of Guam, as revealed in records of the Japanese invaders and in post-war accounts by American and Japanese officers.

Throughout 1941 Japanese ships and planes from Saipan kept close watch on Guam. This vigilance increased in the latter part of the year, for the Japanese feared that America might reinforce the garrison at the last minute. Saipan's small 18th Naval Air Unit began regular reconnaissance flights in the middle of October, flying no closer than 30 miles offshore, and watched for shipping arrivals and departures. Ships from Saipan also joined in the hunt for intelligence, and the Saipan garrison even established a little lookout station on Rota, only 49 miles from Guam which was visible on a clear day. The Guam garrison was well aware of these activities and on one occasion an American patrol boat dashed out to intercept a Japanese ship, but the vessel made for Rota at high speed and got away.

The report submitted by Japanese fliers at the end of November shows what Guam looked like to its invaders, and is worth quotation at length:

"1. Anchored in Apra Harbor are I tanker, 1 ship that looks like a gunboat and 2 small vessels.

"2. There does not appear to be any airfield and no planes (land or seaplanes) were sighted.

"3. The locations and numbers of gun positions are unknown, and the number of troops is also not clear; but, judging from the accelerated road construction, etc., it appears that preparations of lookout posts and gun positions may be considerable. . . .

"4. The barracks, cable station and fuel tanks on Orote Peninsula, as well as the Naval Repair Station, wireless station and other prominent targets were spotted.

"5. No enemy surface or air movements were noted in the area."

This report was comprehensive and correct in most particulars. The ships in Apra Harbor were tanker R. L. Barnes, minesweeper Penguin, and 2 patrol boats. The only air installation was a seaplane stopover used by Pan American Airways. The "prominent targets" noted included almost everything of military significance. But the references to gun positions were unjustified, for there was no fixed or field artillery on the island, except two 3-inch antiaircraft guns on Penguin. Indeed, Guam was even weaker than the Japanese report indicated.

Invasion planners made a fairly accurate estimate of 300 men as the combat strength of Americans on Guam. Actually, there were 153 Marines, 271 Navy personnel and 134 civilian construction workers and Pan-Air employees, under Capt George J. McMillin, USN who was both island commandant and civil governor. This tiny garrison was not, however, intended to be an adequate defense force, for the Marines and Navy men were only enough to provide a civil government, police and a medical staff for almost 24,000 natives. Moreover, the garrison had only small arms and 4 .30 caliber machine guns.

But the Japanese made a substantial error in estimating the strength of native troops at 1,500. Actually there were only 80 Guam natives in the Insular Force Guard, and these were recruits with less than a year's training. This over-estimate, added to their failure to realize that the garrison had no fixed defenses, artillery or even mortars, induced the Japanese to earmark 6,000 men in ground troops alone for the invasion of Guam.

A 5,500-man regimental combat team, called the South Seas Detachment and commanded by MajGen Fomitaro Horii, formed the bulk of the invasion force. Specially organized to seize Guam and later the Bismarcks, the RCT included a headquarters, infantry regiment, mountain artillery battalion, engineer company, part of a cavalry company (mounted), antiaircraft company, antitank gun section and various service troops. To this substantial force the Imperial Navy added 400 sailors, trained as marines, from the Saipan garrison. This detachment was led by Cdr Hiroshi Hayashi, and known as the Hayashi Detachment. Hayashi's unit was to garrison the island after its capture, though it was also to play an important role in the invasion itself.

The Japanese also committed considerable surface strength to the Guam invasion, including heavy cruiser Aoba, destroyers Yuzuki, Kihuzuki, Uzuki and Oboro, 12 transports, 4 gunboats, 5 subchasers, a minesweeper squadron and other auxiliaries. All vessels, except 9 army transports, were drawn from the Japanese Fourth Fleet, which commanded the Mandated bases that surrounded Guam. Fourth Fleet CinC, Adm Nariyoshi Inoue was responsible for the Guam operation, though General Horii would take over once the troops landed.

On 8 November 1941 Gen Horii received orders from Imperial GHQ to ready his South Seas Detachment for the invasion of Guam. A week later Adm Inoue flew from the Mandates to Iwakuni Air Base in Japan, where he and Gen Horii conferred for 2 days. Here they ironed out the details of Army-Navy co-operation and set a schedule for the advance on Guam, which they timed so that the invasion force would appear off Guam almost at the very moment of the Pearl Harbor attack. The army transports with the South Seas Detachment aboard would leave Japan and rendezvous with Fourth Fleet ships in the Bonins. Then the combined force was to head for Rota in deepest secrecy, to a second rendezvous with auxiliaries from Saipan bearing the Hayashi Detachment. Only the appearance of American planes over Guam or the compromise of secrecy would change this plan.

On 20 November Horii issued a detailed operations order, including the landing plan, and directed his RCT to embark for movement south. His transports reached Hahajima in the Bonins by the end of the month, where they rendezvoused with Aoba and other ships on 2 December. On the same day Horii received an order from Imperial GHQ setting D-Day on Guam at 10 December. The combined force departed Hahajima on the 4th, moved slowly and cautiously southward and reached Rota before dawn on the 8th. Here they met the auxiliaries from Saipan, carrying the Hayashi Detachment and towing landing barges. The troops settled down in their transports to wait for D-Day, as escort vessels fanned out on antisubmarine patrols.

While the small task force made its way toward Guam, a much greater force crept up on Hawaii. At 0750, 7 December in Honolulu (0420, 8 December on Guam) the first wave of Japanese planes struck Pearl Harbor. Forty minutes later the 18th Naval Air Unit on Saipan was ordered to attack Guam.

The Naval Air Unit, which had only about a dozen planes, was to carry out 3 important missions during the 8th and 9th. First, sink the "Guam Navy," second, bomb installations ashore and third, make a final report on the defenses of the island.

The first flight from Saipan sighted Guam at 0800 on the 8th. The pilots searched carefully for signs of aircraft and finding none, moved in on the tanker, Barnes. The ship could not even move under her own power and was kept moored to her buoy as a floating oil tank. The planes dropped 10 bombs over the sitting duck and near misses started several leaks in her hull. Next the planes turned on Penguin which had steamed to open sea at the harbor entrance. The crew manned their guns in the teeth of strafing that killed one and injured several, but Japanese bombs soon put the ship in a sinking condition. The sailors entered life rafts, and Penguin went down in deep water off Orote Point, taking Guam's only artillery with her. The planes attacked the remaining ships that afternoon and on the 9th, and by evening of the second day the "Guam Navy" was no more. Penguin was sunk, Barnes was a riddled hulk, one patrol boat was destroyed by fire and the other severely damaged.

The pilots concentrated their attacks on Guam itself in the area from Agana to Orote Peninsula, where all important military and civil installations were located. Heavily populated Agana was the island capital and headquarters for the garrison. Orote Peninsula held the Marine Barracks and the cable station, and the shores of Apra Harbor contained the remaining installations of military significance, including the Navy Yard at Piti.

First shore target the morning of the 8th was the Marine Reservation and several Marines were hit. During the day the reservation, cable station, Navy Yard and radio station were bombed and strafed. A cache of fuel drums near the cable station was hit and burst into flames. Bombs fell on civilian houses and the PanAir Hotel. On the second day the pilots bombed the same targets and strafed lookout stations and native villages at scattered points. The defenders answers back as best they could with rifle and machine gun fire, inducing the pilots to maintain respectful altitudes. They even hit the fuel tank of one plane, but the pilot was able to make it back to Saipan.

At 2109 9 December the 18th Naval Air Unit made its final report. No gun positions throughout the length and breadth of the island. No mines in any of the harbors or bays. The only defense installation was a supposed machine gun position in the northern suburbs of Agana.

With the island softened up by 2 days of bombing and strafing, Horii's landing plan was ready for execution. His plan called for seizure of the Agana-Orote area by converging attacks from the north and south. He divided his forces into 3 parts, and ordered each to land on widely separated beaches and converge on the Agana-Orote area. One part was to land north of Agana, another far south of Orote and the third on the east coast. The landing plan, with a partial breakdown of the forces assigned to each beach, is shown on the map (page 20).

The northern landing force was composed of a reinforced battalion, called the Tsukamoto Force, and the Hayashi Detachment. Both were to land through an opening in the coral reef in Tumon Bay at 0230. The Tsukamoto Force was to move rapidly down the coast, seize Agana, and then occupy the high ground inland as far south as Mount Chachao. The Hayashi Detachment was to remain under command ol the Tsukamoto Force until the capture ol Agana. Then Hayashi was to continue along the coast, seize installations on the shore of Apra Harbor, meet the southern landing force, and support its invasion of Orote Peninsula. Hayashi could call on the Tsukamoto Force for help if strong American resistance developed.

The remainder of the South Seas Detachment, called the Kusunose Force and amounting to two-thirds of an RCT, was committed to the southern and eastern landings. The exact division of troops for each beach does not appear in Japanese accounts, but they were divided into a Main Body for the southern landing, and a Detachment for the eastern landing. The Main Body was to land on an open beach north of Merizo, advance north along the coast to meet Hayashi between the neck of Orote Peninsula and Cabras Island, and then take the peninsula itself. The Detachment was to land at Ylig Bay and occupy high ground south of the area taken by the Tsukamoto Force. Both landings were scheduled for 0430.

Support vessels were to shell suspected shore batteries (in spite of the negative reports of the planes) and points of expected resistance, especially along the west coast from Merizo to Orote, which was the proposed line of advance of the Kusunose Force Main Body. They would not attempt to soften up the landing beaches, for all landings were scheduled before dawn (0530) and night bombardments were expressly forbidden. The planes from Saipan were assigned similar targets and were to lend close ground support in case resistance developed.

Horii himself was to land with the southern landing force and accompany it to Agat where he would establish his headquarters. He expected the strongest American resistance to form on the narrow front afforded by Orote Peninsula, and planned his elaborate maneuvers to end with a strong drive to crush the defenders there. With his headquarters at nearby Agat, he would be in position to command the final push in person. His assumption that the main resistance would be on Orote was well founded, for the Marines under LtCol William K. MacNulty, less 28 men on patrols at scattered points, took up positions at the butts of their rifle range near Sumay. The Insular Force Guard, however, formed in Agana Plaza, and Capt McMillin kept his headquarters at Government House in Agana.

By 0100, 10 December the transports and escorts moved to assigned positions off the beaches and began to ready landing barges and ships' boats. Soon the northern landings began. The Tsukamoto Force found the hole in the fringing reef of Tumon Bay and hit the beach at 0225, 5 minutes ahead of schedule. But the Hayashi Detachment, which started from a different ship, somehow missed the reef opening in the dark. The navy men then followed the reef south looking for a passage, but when the reef ended they were confronted by the steep cliffs of the promontory that divided Tumon and Agana Bays. Hayashi's men finally rounded this promontory and entered Agana Bay itself, where they discovered a suitable channel at Dungcas Beach. The sailors used flares to guide themselves ashore and thus destroyed any chance of surprise. About 0400, Capt McMillin, only 2 miles away in Agana, received word that flares had been spotted at Dungcas Beach.

The Tsukamoto Force had not yet reached Dungcas Beach, perhaps because it waited for Hayashi to appear in Tumon Bay. According to plan Hayashi should have waited for the army unit to catch up, but instead he decided to attack Agana all by himself. He led his men over a dirt road along the shore and soon found a good surfaced road leading straight to the capital. He met his first resistance in the suburbs, but forced the defenders (their identity is unknown) to retreat and pushed on toward the plaza and the waiting Insular Force Guard.

When Hayashi's men reached the plaza at 0515, a burst of fire from the opposite side halted their advance. A brisk firefight began, but it was soon apparent to the defenders that they were no match for 400 well-equipped Japanese. By 0545 Capt McMillin had received word of the army landings and realized that further fighting could only lead to useless slaughter. He notified the Marines on Orote that they should offer no resistance. At the same time 3 blasts on the horn of an automobile parked before Government House were taken by both sides at the plaza as a signal to cease fire.

A Japanese then shouted across the plaza, "Send over your Captain!" Commander Donald T. Giles and BMC Robert B. Lane stepped out into the open, and were marched behind Japanese lines to meet Hayashi. About 0645 they returned with the Japanese commander to the plaza, where many Americans and the native soldiers were herded together under cover of Japanese machine guns. Commander Giles identified Capt McMillin and both entered Government House with Hayashi to discuss a formal surrender. But they had no interpreter, for the Japanese had not planned that Hayashi would be in this position. So Hayashi selected his own interpreter from the resident Japanese nationals who had been kept in the Agana jail since the 8th. After a briet discussion, Capt McMillin wrote and signed articles of surrender. The Japanese flag rose over Agana.

After accepting the surrender, Hayashi continued to move over a good surfaced road along the coast. He took the Navy Yard at Piti, but soon after ran into men from the Insular Patrol. The Marines fired on the advancing Japanese, but were soon overwhelmed and taken prisoner. Still moving at a fast pace, the Hayashi Detachment proceeded to the neck of Orote Peninsula without contacting the southern landing force whose attack on the peninsula he was to support. Again Hayashi decided not to wait and advanced on Col MacNulty's Marines, who had been ordered to offer no resistance. He accepted their surrender at 1025 and it was all over.

Six hours after landing at Dungcas Beach, Hayashi had more than accomplished his mission, but where was the South Seas Detachment? The Tsukamoto Force was far behind Hayashi, and the other forces were bogged down in the boondocks miles away. The eastern landing force missed Ylig Bay, and instead landed at Talofofo Bay, which was farther from their objectives. The force was then confronted with an uphill climb cross country or along tortuous trails that obstinately refused to go in the right direction. The southern landing force split into 2 parts. One took an inland trail over rugged, jungled and mountanious terrain. The other followed a combination of trails and roads near the cost that crossed at least 20 stream beds from the landing beach to Agat. The Japanese certainly picked some difficult routes to their main objectives.

When American forces re-took the island in 1944, the 3d Mar Div and 1st ProvMarBrig smashed over the reefs at Asan and Agat, cut off Orote Peninsula, and pushed the Japanese back into the jungled interior. Why did Horii not suggest such a plan? The answer lies partially in the coral fringing reefs that girdle Guam. Horii selected landing points where channels made access easy. It must be remembered that the Japanese had only simple landing barges and ships' boats, nothing at all resembling the amphibious tracked vehicles that later made it possible for American assault forces to get over coral obstacles.

However, this is not the full explanation, for there were reef openings closer to the Agana-Orote area than those Horii adopted. Remember that he greatly overestimated the strength of the Insular Force Guard and remained convinced that the defenders possessed shore batteries in spite of the failure of air reconnaisance to locate any with certainty. He could not rely on his small surface and air strength to soften up the beaches effectively and dreaded the thought of assault landings in the face of American fire. From Horii's point of view, assault landings were perilous and unnecessary and he decided to put his troops ashore at remote points where he believed they would run into little or no opposition. To guarantee that his landing operations would come off undisturbed, he conducted them at night.

It is hard enough to get troops ashore with reasonable order in daylight and darkness increases the difficulty. As might be expected, some of the landing troops did miss their beaches, with results that changed the entire character of the operation. Hayashi stumbled onto a direct approach that ended the operation quickly, while the army units contributed little more to the capture of Guam than to convince the Americans of its inevitability.

Once the overwhelming Japanese forces were ashore, the tiny American garrison had no choice but to surrender. In 2 days of bombings and in the fighting on the 10th, the Navy and Marine Corps lost 13 dead and 37 wounded, the Insular Force Guard 4 dead and 5 wounded, and Japanese sources indicated 40 to 50 native civilians had been killed and many wounded although McMillin officially reported only 7 civilian casualties. Further resistance would risk not only the lives of the garrison, but the lives of many more innocent civilians. The American survivors, who spent the next three and a half years in Japanese prison camps, might take grim consolation in the thought that their very presence on Guam tied clown 6,000 first-class Japanese combat troops, a cruiser and many supporting ships.

The Hayashi Detachment became the pride of the Imperial Navy. But their pride lasted no longer than Japan's hold on Guam. When the Marines landed in 1944, the Hayashi Detachment, still on the island, was annihilated.