Technical Specifications


Wa-1 Auxiliary Minesweeper


9 November 1941


31 January 1942




222 tons


97 feet (29.6 meters) waterline 


19 feet 5 inches (5.8 meters)


7 feet 10 inches (2.1 meters)


1-shaft, Diesel Motor


unknown capacity

Shaft Horse Power





1700 @ 9.5


40-cal Type 3 (1914) 8-cm [76.2mm/3-inch] HA gun, 6 DCs, small machine guns like 7.7mm calibre Type 92

Site Location
U.S. Navy Action Report says “5 miles NE of Savo Island” or “5 miles ENE of Savo Island”. But this site maybe closer to Tulagi and less than 100 meters depth (see Wa-2 for discussion).
09º 3.000’S, 159º 52.500’E. Derived from map of attack and location statements as above. Plotted distances from Savo Island on Google Earth.
Site Depth
990 meters (3247 feet) estimated from chart BA1713
Site Creation and History
Wa-1 was the first of a class of 22 wooden auxiliary minesweepers built under 1940 and 1941 programmes. They were based on proven trawler hull designs. The two sister minesweepers Wa-1 and Wa-2 were assigned to Rear Admiral Shima Kiyohide’s Tulagi Invasion fleet along with the four other converted minesweepers. Besides being used as general utility vessels in the area, the Japanese were well prepared if the Allies had minefields in the Tulagi and Gavutu Harbours. As it turned out on 3 May 1942 when the Japanese force captured the area, there was no minefields and indeed no defence of the region at all, as the token Allied force had abandoned the area the night before.

Japanese Tulagi (RXB) Invasion Force 2-4 May 1942


4400 tons Minelayer (Flagship)
Landed: 3rd SNLF


1772 tons Destroyer (Destroyer Division 23)


1772 tons Destroyer (Destroyer Division 23)

Azumasan Maru

7623 tons Navy Transport

Landed: Kure 3rd SNLF; Civilian Hashimoto Construction Force; Mitsuwa Antiaircraft unit; 7th Construction Unit Detachment. Cargo: Air Base Equipment (probably aviation fuel in drums, seaplane moorings, trolleys, equipment, tools, etc)

Tosan Maru

Landed: Kure 3rd SNLF

Koei Maru



222 tons Auxiliary Minesweeper


222 tons Auxiliary Minesweeper

Tama Maru

264 tons Converted Minesweeper

Minesweeper Division 14; Ex-steam whale catcher.

Tama Maru No. 8

Converted Minesweeper

Antisubmarine Boat Group 56; Ex-steam whale catcher.

Toshi Maru No. 3

Auxiliary Submarine Chaser

Antisubmarine Boat Group 56

Hagoromo Maru

234 tons Converted Minesweeper

Noshiro Maru No. 2

216 tons Converted Minesweeper































Total : 13 vessels

On the 4 May 1942, the day after the Japanese captured Tulagi, American aircraft from the carrier U.S.S. Yorktown (CV-5) conducted three air attacks on the Japanese shipping in the area. On the second air attack mid-morning by SBD-5s of Bombing Five (VB-5), the Dauntless dive bombers found “three gunboats” steaming away from Tulagi between Savo Island and the Northern end of the Florida Islands. The “three gunboats” as the American pilots referred to them, were probably Wa-1, Wa-2 and Tama Maru. No doubt the three minesweeper captain’s had the throttle’s wide open since the first attack, and hurriedly departed Tulagi, but all they could muster was a sedately 9-10 knots. They were fleeing Westwards trying to get the hell away from all the bigger military targets in the Tulagi Harbour area like the Azumasan Maru anchored in the middle of Tulagi Harbor and the big minelayer Okinoshima which looked like a heavy cruiser. By the time the 2nd air attack rolled in, the little minesweeper convoy had only reached the vicinity of Savo Island. No less than 14 Dauntless SBD-3 dive bombers attacked the little minesweepers, and Wa-1 and Wa-2 with wooden hulls disintegrated in the blasts of 14, 000 pounds of Mark 13 high explosives fuzed with Mk 21 and 23 fuzes. Incredibly, the third minesweeper was only near missed, and limped away, but the Dauntless’s expended 2900 rounds of 50-calibre and 1200 rounds of 30-calibre machine gun ammunition, much of which was expended in trying to sink the 3rd “gunboat”. This “lucky” third gunboat must have been the 1936 vintage steel steam whale catcher Tama Maru, and severely damaged, the skipper headed for the nearest land…Naghotano Island in the Northern Floridas where a successful beaching was made. The Koei Maru steamed out to the grave site of the Wa minesweepers and picked up survivors.
On nearby Savo Island, the roar of American carrier bombers flying over and the boom and rattle of exploding bombs and machine gunning would have been a truly awe-inspiring sight to the native Melanesians. This was the first instance of fast single-engine carrier planes in the area and the first sighting of American planes. The local population since February 1942 had seen plenty of the big lumbering Kawanishi MAVIS flying boats on recon and bombing Tulagi and Gavutu. After the action of 4 May, the American carrier planes would not be seen again until 3 months later at the 7 August 1942 landings in the area. On Savo, there were two other historical witnesses. One was coast watcher Leif “Lafe” Schroeder. Pre-war he ran a trading store on Savo Island, and when the war began, the RAAF contingent based at Tanambogo provided him a radio and asked him to warn them of approaching Japanese aircraft. He had plenty to report on May 4. Somehow he reported ten ships sunk and a “cruiser” beached on Naghotano Island. Lafe’s teleradio reporting was somewhat troubled as he was almost deaf. The other witness was Native Medical Practitioner (NMP) George Bogese. Two Japanese sailors from the sunken Wa minesweepers somehow crossed the five miles or so and reached Savo’s shores. Despite being warned by Lafe, Bogese went to them and tended their sufferings. Having revealed his skills, when the Japanese soon came calling, he was taken away with them and the Japanese would evidentially obtain much intelligence from Bogese. Bogese remained with the Japanese on Tulagi until captured by the 1st Marine Raiders in the 7 August 1942 Tulagi assault.
Archaeological Notes
This site has not yet been located (2011). It is unlikely it will be a search target for many years unless on the shallow “Florida Shelf”. There are far larger and more significant WWII naval sites in the vicinity.
As these vessels were severely damaged during the attack and constructed of wood, the archaeological site is going to be small and not very pronounced. The most prominent parts of the wreck will be the ready ammunition boxes on the bow stocked with 3-inch ammunition, anchors & chain, the 40-cal Type 3 (1914) 8-cm HA gun on the bow, the 300 HP diesel motor, prop shaft & propeller and depth charges/racks at the stern.  The wooden hull will have totally disintegrated and been eaten away by shipworms, particularly the Toredo Navalis, down to the mud seafloor level. It is quite possible the keel area and hull below the mud level is well preserved by anaerobic conditions. Areas of wood in contact with metal also tend to be better preserved. Were these minesweeper hulls copper sheathed? Archaehistoria has found that on old wrecks with copper sheathed hulls, the wood immediately inside the copper sheathing is better preserved by the toxic effects of the copper.
The Wa-1 was practically a new vessel when lost. She was only about 6 months old when sunk.
Ecological Threat
This site is a small one and ecological threat from leaching hydrocarbons is small. It is likely the fuel cells in this vessel suffered battle damage and the diesel fuel at the time of sinking was thus mostly removed and evaporated.
Warships of the Imperial Japanese Navy, 1869-1945 by Hansgeorg Jentschura, London: Arms & Armour Press, 1977, 284pp.
Request for Information
Archaehistoria would be most grateful for any historical material relating to the Wa-1 class of minesweeper and the 4 May 1942 action. Are there any photographs of the Wa-1  class?


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