On Nov. 2, 1945, as part of the Hagana's “The Night of the Railroads” large scale operation against the British, a squad that had been formed for the occasion by the Palyam penetrated the port of Haifa and blew up two Police shore patrol boats. Another Palmach fighter blew up a third patrol boat in the port of Jaffa. These patrol boats bore the brunt of the British operations against the Aliya Bet vessels until the British Navy’s “Palestine Patrol” was formed and activated. This was the first time that British vessels had been sabotaged by underwater actions.

The operation in the port of Haifa was carried out by the Palyamniks Yochai Ben-Nun - the squad leader, Yigal Weiss and Shaul Oren. They swam to the bottom of the boats and attached home-made mines which were made from combustible materials stuffed into the tube of a motorcycle tire. This was attached to the boat by a contraption that had been made in the workshop of Kibbutz Sdot Yam. The “job” in the port of Jaffa was accomplished by the Palmachnik Zalman -"Zome" - Cohen. He was brought to the vicinity of the port by a small life-saving boat operated by Yossi Harel and then swam among the Arab fishing boats until he reached the Police boat.

  Yochai Ben-Nun - Ha'Chulya's commander

The explosions occurred in the early hours of the morning and rocked the port areas. The patrol boats were severely damaged. The British were quite certain that the work had been done by professionals who had modern equipment, so they started to take extreme measures of caution in guarding their boats and ships. They docked them as close as possible to the port police stations, and the areas around them were flooded with searchlights and surrounded by metal nets; the surrounding areas were constantly patrolled by small boats which would also set off depth charges from time to time, in order to deter swimmers and divers.

The success of these first underwater sabotage operations encouraged the Palmach’s command, and it decided that a permanent underwater sabotage squad should be established as part of the Palyam, with Yochai Ben-Nun as its commander. The base of the squad was at the main Palyam's base in Sdot Yam. Yochai described the early days of the unit in these words: “We had no rubber suits, no fins no underwater equipment, not even a snorkel; and we had no fast getaway boat…”. The unit, comprising a permanent core of 5 – 6 men, became known as “Ha’Chulya” (“The Squad”). At the beginning of every operation Yochai would scrounge around for additional Palyamniks he would need to support the job in hand.

In the Book of the Palmach (1957), Yochai mentioned the following Palyamniks with respect to Ha'Chulya's activities (the list includes both the core & the supporting persons): Shlomo Kimchi, Moshe Nachshon, Izzy Rahav, Gershon Agmon-Karlinsky, Gideonchik Rosen, Shaul Oren-Aharonov, Yossale Dror-Huber, Ossie Ravid-Shmukler, The Redhead Moshe Chadad, Misso Abarbanel, Yehuda “Pere” Ben-Tzur, Yoske Rom-Romanovsky, Eliyahu “Garbo” Glaser, Yigal Weiss, “Eskimo” Aharon Ben-Yosef, Meirke Avraham, Chaim “Vinkie” Vinkler, Uzi Sharon, Avraham Chen, Yona Fodor, Benny Kravitz, Gideon Vaadi and Gavriel “Gavrosh” Rapaport.

In the course of 1946-47 Ha'Chulya successfully carried out the following sabotage operations against British targets:

• Sabotaging the deportation ship Empire Haywood in the port of Haifa (Aug. 18, 1946)

• Sabotaging the deportation ship Empire Rival in the port of Haifa (Aug. 22, 1946)

• Sabotaging two barges that were used as floating bridges to move ma’apilim (illegal immigrants) onto the deportation ships sailing to Cyprus and a patrol boat in the port of Haifa (Feb. 13, 1947)

• Sabotaging the deportation ship Ocean Vigor in the port of Famagusta, Cyprus (Apr. 2, 1947)

• Sabotaging (again) the deportation ship Empire Rival on her way to Egypt (Apr. 4, 1947)

• Sabotaging the deportation ship Empire Life Guard in the port of Haifa (Jul. 23, 1947)

In Sep. 1946, an operation with a potential for a big impact, to sabotage a destroyer at the refueling pier in the port of Haifa, failed.

The focus of Ha’Chulya's operations shifted from Palestine to Cyprus in Apr. 1947. This was the result of the tight security of the British naval installations in Palestine, and the opportunity to utilize the Cyprus Detention Camps as base for operations.

In 1948, two small units whose roots were in Ha’Chulya were added to the newly-born Israeli Navy – underwater sabotage under the command of Yossale Dror, and the explosive-speedboats unit (deployment of boats loaded with explosives; the boat operator had to direct it at the enemy ship and jump off at the last minute to save himself) under the command of Yochai Ben-Nun. The units were united into one on January 1st, 1950, to became the famous “Shayetet 13” - the Israeli Naval Commando (Navy Seals; the number '13' is traced to the Palyamniks' tradition to drink a glass on the 13th of each month).