The Battle off Endau was a Second World War battle that took place off Endau town on 26–27 January 1942. Part of the Battle of Malaya, it was the first notable naval engagement since the sinking of the battleship Prince of Wales and the battlecruiser Repulse on 10 December 1941, and the last effort by the Royal Navy to intercept Japanese convoy shipping around the Malay Peninsula.

A Japanese convoy approaching Endau was detected by reconnaissance aircraft on 26 January and was ineffectually attacked multiple times by Allied aircraft as it was landing its troops. The Allies suffered heavy casualties, while the Japanese lost only a single aircraft. The Royal Navy committed two destroyers later that day to break up the Japanese landings, despite the much larger Japanese escort force. Sailing under the cover of darkness, they were able to locate the convoy anchored there without being detected, but could not find the troopships in the darkness. The ships attempted to disengage, but were fired upon by the convoy's escorts and one destroyer was sunk in the early morning hours of 27 January.

The sinking of Prince of Wales and Repulse in the opening stages of the Malayan Campaign left the task of intercepting Japanese convoys in the Gulf of Siam to the submarines of the Royal Netherlands Navy as the surface ships were occupied escorting Allied convoys to and from Ceylon and the Dutch East Indies. The Dutch recorded their first success when the troopship Awazisan Maru was sunk off Kota Bharu on 12 December 1941, probably by HNLMS K XII. On 24 December, HNLMS K XVI sank the destroyer Sagiri off the coast of Kuching, Borneo. Several other vessels were also damaged or sunk during the early weeks, but losses were high for the Dutch submarines and they could do little to stem the Japanese advance.

An amphibious landing at Mersing was originally planned by the Japanese to sever the lines of communication between the British forces and Singapore, but the Southern Expeditionary Army Group decided to land the rest of the 18th Division at Singora instead, believing that the Allied defences at Mersing were too formidable. Although ground forces captured Endau on 21 January, they lacked the strength to break through the Australian defences at Sungei-Mersing.

On 20 January 1942, a convoy of eleven troopships departed Cam Ranh Bay, Indochina, to unload ground forces at Singora, of which two would proceed to Endau. The two transports, Kansai Maru and Canberra Maru, were carrying troops of the 96th Airfield Battalion, assigned to bring the airfields of Kahang and Kluang into operation. They were escorted by the 1st Escort Unit, which was formed around Torpedo Squadron 3, which consisted of the light cruiser Sendai, flagship of Rear-Admiral Shintarō Hashimoto, and six Fubuki-class destroyers, Fubuki, Hatsuyuki, Shirayuki, Asagiri, Amagiri, and Yūgiri. The squadron was augmented with the five W-1-class minesweepers of the 1st Minesweeper Division, three CH-4-class submarine chasers of the 11th Submarine Chaser Division, and four converted patrol boats.

Malaya Command anticipated that the Japanese force would soon be reinforced by a naval convoy, a suspicion confirmed on 26 January when two Royal Australian Air Force (RAAF) Lockheed Hudson aircraft sighted them 20 miles (32 km) north of Endau. Although they spotted the Japanese convoy at 07:45, their radio transmissions were jammed, and news did not reach higher command until they landed in Singapore at 09:20. The RAF decided to attack the convoy with all available aircraft. The attack had to be delayed until that afternoon, however, to allow the crews of the Vickers Vildebeest and Fairey Albacore torpedo bombers of No. 36 Squadron RAF and No. 100 Squadron RAF to rest after their night missions. The decision to use the elderly Vildebeest biplanes against the ships in daylight came as a shock to the pilots, who had been restricted to the relative safety of night sorties following the first day of the invasion.

The first air attack was carried out by the Vildebeests of Nos. 36 and 100 Squadrons and the Hudsons of Nos. 1 and 8 Squadron RAAF. Twelve Vildebeests and nine Hudson bombers took off from Singapore in the early afternoon of 26 January, with a fighter escort composed of twelve Brewster F2A Buffalos and nine Hawker Hurricanes. The Japanese landings on Endau had been in progress for over four hours by the time the planes arrived at 15:00. The Japanese naval force had air cover consisting of 19 Nakajima Ki-27s from the 1st and 11th Squadrons and a single Nakajima Ki-44 fighter. Despite heavy opposition, the two transports were bombed, and men and equipment on the beach were strafed. Five Vildebeests were lost in the attack, including the commanding officer of No. 100 Squadron, while one Ki-27 was shot down.

A second wave set off from Singapore at 16:15, consisting of seven Vildebeests and three Albacores of No. 36 Squadron and two Vildebeests of No. 100 Squadron. They arrived over Endau at 17:30, but their escort of seven Hurricanes and four Buffalos were late and the British biplanes were set upon by ten Ki-27s and two Ki-44s before their escorts could reach them. Five Vildebeests, two Albacores and one Hurricane were lost from this wave. Of the 72 aircrew from Nos. 36 and 100 Squadrons who participated in the raids, 27 were killed, seven were wounded and two were captured. The returning pilots were congratulated by Air Vice-Marshal Paul Maltby, who promised them that further daylight attacks were unnecessary.