Komatsu amphibious and underwater bulldozers

History

According to a 2013 paper by engineers of Asunaro Aoki Construction in the journal of the Japan Construction Machinery and Construction Association, development began under the guidance of Japan's Ministry of Construction. The earliest machine it describes, the D125-18B of 1968, could work in 3 m (10 ft) of water ^[4]. It was first used in 1969 for emergency repairs to a sinking bridge pier at the Toyama Ohashi bridge, a job later described as the first case of remote-controlled, unmanned construction ^[4]. In 1971 the D125W-2 raised the working depth to 7 m (23 ft), the larger D155W followed the same year, and an improved D155W appeared in 1976 ^[4].

Komatsu itself dates the amphibious bulldozer to 1971, when it began series production after the 1970 world's fair in Osaka, and it describes the D155W as the first amphibious bulldozer offered commercially anywhere ^[1][3]. Thirty-six were built, and production ended around 1993 ^[1][7]. Fourteen went abroad, to buyers in the Soviet Union, Czechoslovakia and Italy among others ^[1]; the Asunaro Aoki engineers also list Pakistan ^[4]. In 1976 Komatsu demonstrated a D155W in the Elbe River about 30 km (19 mi) northeast of Prague ^[1]. Trade press accounts differ on the details: a British blog gave 1972 for the D155W's first appearance and said the earlier D125W used a Cummins engine ^[5].

Design and how it works

The D155W is more than a sealed land dozer. Its engine sits in a watertight compartment and breathes through a tall stack that carries intake air and exhaust above the surface ^[1]. The drive housings are pressurized automatically to match the water pressure outside, a lamp and horn on the stack warn the operator if water reaches the engine room, and a pump then starts to drain it ^[4]. The stack can be lowered so the machine can work under bridges ^[4].

The operator drives from the bank by radio ^[6]. The paper explains that remote control was used from the start because an operator cannot see the bottom and should be kept out of currents and waves; the current radio works within about 100 m (330 ft), and if it fails underwater a diver can drive the machine by cable from a panel on its body ^[4]. The dozer weighs 43,500 kg (95,900 lb) on land but only 27,900 kg (61,500 lb) submerged. It carries a 4 m (13 ft) blade with hydraulic aprons that stop loosened soil from drifting away, and a rear ripper that can break rock underwater; a crane can be fitted in place of the ripper ^[4].

Use in Japan

Asunaro Aoki took its first machine in 1971, starting with dredging at Omaezaki port in Shizuoka and river work on the Sagami River, and had bought 17 by 1996 ^[4]. Jobs have included fishing ports, sea-urchin and abalone beds off Iwate from 1973, offshore breakwaters in Fukushima from 1975, beach work and river channel excavation ^[4]. On the Shonai River in Nagoya, deepened after the 2000 Tokai floods, about 370,000 m3 (484,000 cu yd) of excavation was planned or under way by 2013 ^[4].

After the 2011 earthquake and tsunami the dozers helped with recovery. They placed bagged stone around scoured piers of the Yuriage Bridge on the Natori River, cleared scattered breakwater blocks and debris from harbors, and rebuilt the Iwate shellfish beds ^[4]. To keep the aging fleet working, Komatsu rebuilt a 1993-built D155W at its Osaka Plant from January to September 2012, ordering 3,458 parts and redrawing about 250 designs, and the machine began work in the disaster area in January 2013 ^[1]. Komatsu says the five machines still in operation are all owned by Asunaro Aoki, which reports more than 1,200 underwater construction projects ^[2].

Electric successor

In August 2023 Komatsu and Asunaro Aoki announced an exhibit on future underwater construction for Expo 2025 in Osaka, built around electric machines that could be run remotely and, in time, work at depths of up to 50 m (164 ft) ^[2]. A battery-powered concept machine was built in July 2023 and tested in rivers and fishing ports ^[3][8]. Komatsu describes it as a robot that operators without special skills can run from a distant office, helped by automatic control and information and communication technology (ICT) functions ^[3].

The machine made its public debut at CES in Las Vegas in January 2025, Komatsu's first appearance at the show. MONOist reported that the unit on the stand was the one used in field trials, rated for 7 m (23 ft) of water ^[8]. The Drive, citing another outlet, reported a 450 kWh battery and a four-hour charge time ^[9]. At Expo 2025 a large model of the concept machine was shown in the Future Life Expo: Future City pavilion, which Komatsu says drew about 1.9 million visitors before the fair closed on October 13, 2025 ^[3][11]. Australian trade press described the project as a step toward automated underwater construction ^[10].

Photos

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