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 . Background . 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 . Prelude . 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 " corvettes 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 . Battle . 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 away from the city of Phan Thiet , and 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 " corvette 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 Brigate , 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 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 . Aftermath . 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 .