At the same time, the Palmach's marine unit, the Palyam, sank three British guard boats; two in Haifa and one in Jaffa. These boats were part of the closure imposed on the shores in order to prevent Jewish immigration. In Haifa Yohai Ben-Nun led the operation and in Jaffa, Yossi Harel and Zalman Cohen did, after a briefing by Yitzhak Sadeh. In both cases the sappers arrived in boats, dived under the British boats and attached explosives with a delay mechanism to the boats.