Israeli authorities say they have located the wreck of the Altalena, an Irgun arms ship at the centre of one of the most divisive episodes in Israel's early history, 78 years after a confrontation with the newly established Israeli military left 19 people dead.

The vessel was found intact at a depth of 503 metres, about 20 kilometres off Israel's Mediterranean coast, following a maritime search involving specialised sensors and survey equipment, according to Israel's Heritage Ministry.

Heritage Minister Amichai Eliyahu described the discovery as a “defining moment for our national memory”.

The announcement was also made by National Security Minister Itamar Ben-Gvir, whose far-right Otzma Yehudit party traces part of its ideological lineage to the Revisionist Zionist movement associated with Irgun leader Menachem Begin.

The ship's location was announced on 24 August after months of planning, although questions remain over how new the discovery actually is. Jewish News reported that the Israeli government had known the wreck's location since 2012, while officials presented the latest operation as conclusively locating and identifying it.

The Altalena arrived off the coast in June 1948 carrying hundreds of immigrants, Irgun members and a large shipment of weapons and ammunition.

Irgun, also known as Etzel, was a Zionist paramilitary organisation that fought British rule in Mandatory Palestine and carried out attacks against British authorities and Palestinians before Israel's establishment.

The ship arrived weeks after Israel declared independence and while separate Jewish armed organisations were being absorbed into the newly created Israel Defense Forces.

A dispute developed between Prime Minister David Ben-Gurion's government and Begin over control of the weapons.

Begin wanted 20% of the arms allocated to Irgun forces operating independently in Jerusalem, with the remainder transferred to the IDF while helping equip former Irgun units incorporated into the military. Ben-Gurion's government insisted that weapons entering the country had to come under the authority of the state and its army.

The confrontation first turned deadly near Kfar Vitkin, north of Netanya, after Israeli troops surrounded Irgun fighters unloading the vessel.

Six Irgun members and two Israeli soldiers were killed there before a ceasefire was reached.

The Altalena subsequently sailed towards Tel Aviv with Begin aboard.

On 22 June 1948, Israeli forces opened artillery fire on the ship off Tel Aviv. The vessel caught fire and those aboard were forced into the water.

Another 10 Irgun members and one Israeli soldier were killed, bringing the overall death toll from the confrontation to 16 Irgun members and three IDF soldiers.

Begin ordered his followers not to retaliate against the Israeli military as fears grew that the confrontation could develop into a wider internal conflict.

The burned vessel remained near Tel Aviv before it was later towed farther out into the Mediterranean and deliberately sunk.

The Altalena affair became an enduring political fault line between Ben-Gurion's Labour Zionist movement and Begin's Revisionist camp.

Begin eventually became prime minister in 1977, ending decades of Labour dominance and bringing Israel's nationalist right to power for the first time.

The wreck's discovery has already become part of contemporary Israeli political rivalry.

Ben-Gvir said finding the vessel carried a message against civil war, while Prime Minister Benjamin Netanyahu separately claimed credit for reviving the search, saying he had ordered renewed efforts and allocated a special budget in 2019.

Netanyahu also said the government intended to raise the Altalena from the seabed. Recovering a vessel from more than 500 metres underwater would require a substantial salvage operation, and no timetable has been announced.

Israeli authorities have released imagery from the latest search operation, including a computer-generated representation of what they identified as the wreck.

The Heritage Ministry says the discovery will be used to preserve the Altalena's history for future generations. No detailed plan for recovering, conserving or displaying the vessel has yet been announced.