East Sea Campaign
The East Sea Campaign was a naval operation which took place during the closing days of the Vietnam War in April 1975. Even though it had no significant impact on the final outcome of the war, the capture of certain South Vietnamese-held Spratly Islands Islands (Truong Sa) in the South China Sea (referred to by the Vietnamese as the East Sea), and other islands on the southeastern coast of Vietnam by the Vietnam People’s Navy and the Viet Cong helped the Socialist Republic of Vietnam assert its sovereignty over the various groups of islands after the reunification of the country in 1975. The North Vietnamese objective was to capture all the islands under the occupation of the Army of the Republic of Vietnam (ARVN), and it eventually ended in complete victory for the North Vietnamese military and their Viet Cong allies.
During the spring season of 1975, as units of the Vietnam People's Army were pushing toward Saigon as part of the 1975 Spring Offensive, the North Vietnamese High Command decided to capture all South Vietnamese-occupied islands located on the southeastern coast of Vietnam, and in the South China Sea. Subsequently, different units of the Vietnam People's Navy (North Vietnam's naval force) were deployed to coordinate their forces with local Viet Cong units in South Vietnam to take the Spratlys, and other territories.
During the 1970s the Spratly islands was already a source of dispute for many countries in the region with Malaysia, the People's Republic of China (Communist China), the Republic of China (Taiwan), the Philippines and South Vietnam all claimed sovereignty over all or parts of the islands. In early 1975 the underlying tension between the claimants came to the surface when South Vietnam invaded Southwest Cay, then occupied by the military forces of its wartime ally, the Philippines. In order to lure the Philippines soldiers off Southwest Cay, it was reported that South Vietnamese authorities sent prostitutes to the birthday party of the Philippine military commander on another island.
While the Philippine soldiers left their post to attend the birthday party of their commanding officer, South Vietnamese soldiers moved in to occupy Southwest Cay. After the Philippines military realized they had lost their territory, they planned to retake the island from the South Vietnamese through military force. However, by the time the Philippines military were able to put their plan into action, the South Vietnamese had already built a strong defense on Southwest Cay, thus deterring any potential counter-attack. Later Southwest Cay would be the first major target for the North Vietnamese Navy.
North Vietnam 
On April 4, 1975, the High Command of the Vietnam People’s Navy and the Command of Military Region 5—under the command of General Chu Huy Man—agreed on a plan to seize some Spratlys and other groups of islands. Under their secret plan, the Vietnam People’s Navy deployed the 126th Battalion, a naval special forces unit of about 170 personnel, to join the Viet Cong 471st Battalion of Military Zone 5. They were supported by three transport ships namely the T673, T674 and T675 along with 60 experienced sailors and technicians from the 125th Naval Transport Brigade. The North Vietnamese operation would commence at 12.00 am on April 9, 1975, to coincide with the North Vietnamese ground attack on Xuan Loc, to take advantage of the hydrological patterns (low tide) in order to land the special forces on the South Vietnamese-occupied sections of the Spratly Islands. To maintain the secrecy of their operation, the North Vietnamese Navy kept their radio communications to a minimum in the days leading up to the attack.
South Vietnam 
Unlike their North Vietnamese counterparts, South Vietnam possessed a large naval force with a strong fleet of ships. Hence the South Vietnamese Navy—commanded by Vice Admiral Chung Tan Cang—were able to maintain a strong presence in the Spratly Islands, with only a handful of infantry units provided by the Army of the Republic of Vietnam (ARVN) to protect the smaller islands surrounding the main Spratly Island To defend the islands, South Vietnamese personnel were mainly equipped with small infantry weapons, as well as the M-72 anti-tank weapon. Whenever necessary, the South Vietnamese Navy could deploy the HQ-4 Tran Khanh Du destroyer, the HQ-3 Tran Van Duat, HQ-16 Ly Thuong Kiet and the HQ-17 Ngo Quyen frigates, as well as the HQ-12 Ngoc Hoi and HQ-14 Van Kiep escort ships to provide fire support. The South Vietnamese Navy also relied on two transport ships, namely the HQ-402 Lam Giang and HQ-403 Huong Giang, to transport vital supplies and reinforcements to South Vietnamese forces on Spratly Island.
Southwest Cay 
On April 9, 1975, three North Vietnamese transport ships, disguised as fishing trawlers, began moving towards Southwest Cay in the Spratly Islands with members of the 126th and 471st Battalions all on board. On the morning of April 11, 1975, helicopters from the United States Seventh Fleet began circling the North Vietnamese transport ships, but they were allowed to move on as the disguised North Vietnamese ‘fishing trawlers’ were mistakenly identified as ships from Hong Kong. After the American helicopters flew away, the North Vietnamese continued sailing towards Southwest Cay. On the night of April 13, the three North Vietnamese transport ships were closing in on Southwest Cay from three different directions. During the early hours of April 13, 1975, North Vietnamese personnel from the 126th Battalion and the Viet Cong 471st Battalion landed on Southwest Cay using rubber boats.
Taken by complete surprise, the South Vietnamese soldiers on Southwest Cay put up stiff resistance, but they surrendered to the North Vietnamese special forces after just 30 minutes of fighting. The North Vietnamese claimed to have counted 6 South Vietnamese soldiers killed in action, and captured 33 prisoners. In response to the attack on Southwest Cay, the South Vietnamese Navy immediately formed a task force which came in the form of the HQ-16 Ly Thuong Kiet frigate and the HQ-402 transport ship to retaliate, but both ships were forced to turn back and defend Namyit Island instead. Having achieved their initial objective, the North Vietnamese naval command sent out the transport ship T641, to carry all the captured South Vietnamese soldiers back to Da Nang. With Southwest Cay firmly in their hands, the North Vietnamese naval command set their sights on the next three targets: Namyit, Sin Cowe and Sand Cay.
Sand Cay 
The North Vietnamese Navy, however, were deterred from attacking Namyit Island because they had lost the element of surprise, as well as the strong presence of several South Vietnamese Navy frigates surrounding that island. So, instead of attacking Namyit, the North Vietnamese selected Sand Cay as their next target. On the night of April 24, under the observation of the Taiwanese military, North Vietnamese transport ships sailed in a single column passed the Taiwanese-occupied island of Itu Aba towards their next objective. Again, following the same pattern of operation, the North Vietnamese transport ship anchored near Sand Cay and prepared for their assault. At 1.30 am on April 25, 1975, three platoons from the 126th Battalion successfully landed on Sand Cay. One hour later, the North Vietnamese 126th Battalion opened their attack and the South Vietnamese were easily defeated, suffering 2 deaths and 23 captured.
The loss of Southwest Cay and Sand Cay, in combination with the defeats suffered by the South Vietnamese Army on the mainland, placed the South Vietnamese Navy in a complex and difficult position. As a result at 8.45 pm on April 26, 1975, South Vietnamese ships in the Spratly Island area were ordered to evacuate the ARVN 371st Local Battalion and withdraw from Namyit and Sin Cowe. While the South Vietnamese Navy were preparing to withdraw from Spratly Island, North Vietnamese Navy reconnaissance units sent reports back to Hanoi, informing the naval command of South Vietnamese ships leaving their positions in Namyit and Sin Cowe. Upon hearing the news of the South Vietnamese withdrawal, the North Vietnamese naval command ordered the 126th Battalion to capture the remaining islands. On April 27 and 28, the North Vietnamese 126th Battalion marched onto Namyit and Sin Cowe without opposition. On April 29, 1975, the North Vietnamese had successfully completed their mission in capturing the key islands of the Spratly group.
Phu Quy Island 
Phu Quy Island, also known as Cu Lao Thu, is located off the coast of southern Vietnam. The island is about 60 nautical miles (110 km) away from the city of Phan Thiet, and 82 nautical miles (152 km) away from Cam Ranh. The island is about 21 square kilometer in size, and in 1975 it had a population of about 12,000 people. At the end of March, 1975, the ARVN maintained a security team on Phu Quy, which included one police platoon and 4,000 members of the civilian self-defense forces. From April, 1975, the local ARVN forces on Phu Quy were joined by an additional 800 South Vietnamese soldiers, who escaped from the mainland town of Ham Tan when North Vietnamese forces captured it. On April 22, the South Vietnamese Navy also deployed the HQ-11 escort ship and one small patrol boat to defend the island from the North Vietnamese onslaught. On April 26, 1975, the Vietnam People's Army South Central Coast Command at Cam Ranh and the 125th Naval Transport Brigade of the Vietnam People's Navy began transporting members of the 407th Special Forces Battalion from Military Region 5, and elements of the 95th Regiment towards Phu Quy.
At 1.50 am on April 27, 1975, the North Vietnamese landed on the island and the fight for Phu Quy Island began. Caught by surprise South Vietnamese units retreated to the administrative center of the island, where they organized their defenses in an attempt to push back the North Vietnamese special forces. While at sea, the South Vietnamese Navy's HQ-11 escort ship clashed with boats from the North Vietnamese 125th Navy Transport Group, but ultimately the long-range artillery used by the North Vietnamese Navy proved too much for the HQ-11 and it retreated from the island with significant damages. After several hours of waiting, the commander of the HQ-11 decided to pull anchor and escaped to the Philippines when further reinforcements from the South Vietnamese Navy failed to arrive. At 6.30 am remnants of the South Vietnamese Army gave up and ended their resistance. The North Vietnamese claimed to have captured 382 ARVN prisoners, and collected more than 900 weapons of various kinds.
Con Dao Archipelago 
Con Dao archipelago is located in the southwestern area of the South China Sea, nearly 180 kilometers (110 mi) from the city of Vung Tau. The Con Dao Island is the largest island with an area of 52 square kilometers, accounting for about 75% of the entire Con Dao archipelago. Con Son is the largest township on the island and was also the seat of the local government. By the end of the Vietnam War, about 7,000 political and military prisoners, of whom 500 were female, were serving their time on Con Dao. On April 29, 1975, the airfield at Con Son became a staging post where South Vietnamese government officials and U.S. advisers from Tan Son Nhat were assembled, to be evacuated to the U.S warships of the 7th Fleet which anchored nearby. During the last days of the war, about 2,000 regular South Vietnamese soldiers were defending the island.
During the early hours of May 1, 1975, all the political prisoners at Prison VII staged an uprising and they quickly overpowered what was left of the South Vietnamese prison authorities. They set up a Provisional Committee to govern the island, and organised three platoon-sized units using captured weapons to march on the remnants of the South Vietnamese army. The political prisoners attacked the ARVN barracks at Binh Dinh Vuong, Camp IV and Camp V. The South Vietnamese Army were easily defeated as they chose to run away instead of fighting back, whilst leaving large quantities of weapons and ammunition behind. Encouraged by the news of South Vietnam's political and military capitulation, the prisoners continued their march towards the local police station which had already been abandoned by the defeated South Vietnamese. By 8am the prisoners had captured all former South Vietnamese infrastructure and assets, including 27 aircraft, as the remaining South Vietnamese Army soldiers at the Con Son airport also surrendered.
On the evening of May 2, 1975, the rebel prisoners on Con Dao Island successfully establish communications with North Vietnamese military units. To prepare for the arrival of the North Vietnamese, the Provisional Committee moved to set up a trench system around the island to defend against a possible South Vietnamese or U.S counter-attack. On the morning of May 5, 1975, the North Vietnamese 171st and 172nd Naval Regiments landed on Con Dao Island with elements of the North Vietnamese 3rd Golden Star Division. Throughout the day regular North Vietnamese military units and the rebel prisoners coordinated their forces, to establish control over the rest of the Con Dao Archipelago.
After more than two months of planning and combat operations, the Vietnam People's Navy successfully captured the Spratly, Phu Quy and Con Dao groups of islands from the South Vietnamese. In the days following their victory the North Vietnamese also went on to raise their flag over the smaller cays and reefs of An Bang (Amboyna Cay), Sin Cowe East and Pearson Reef (Hon Sap). In 1976, following the unification of Vietnam, some Spratly islands became a part of Khanh Hoa Province.
To assert Vietnam's political sovereignty, the North Vietnamese military initially deployed four battalions of the 2nd Division from Military Region 5 to defend the islands. In September 1975 the North Vietnamese Ministry of Defense transferred the 46th Infantry Regiment from the Army's 325th Division to the Vietnam People's Navy, to form a brigade with the 126th Naval Regiment with the purpose of defending the Spratlys and other groups of islands. Following the establishment of the Socialist Republic of Vietnam in 1976, additional units were transferred to 126th Naval Infantry Brigade to bolster the defenses of Vietnam's outlying islands.
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