task units (NSWTU) run by a SEAL commander and answering to the regional naval special warfare task group. Their mission was to stop Iranian forces from mining the Persian Gulf or otherwise attacking shipping. Each mobile sea base had two detachments of Mark III patrol boats, a SEAL platoon, an EOD detachment, Marines to provide security, army MH-6 and AH-6 Little Bird helicopter gunships and Black Hawk rescue birds, and air force combat controllers. Mobile Sea Base Hercules was crewed by East Coast naval special warfare units, including Patrol Boats 777 and 758 from Special Boat Unit 20 and Special Boat Unit 24. Mobile Sea Base Wimbrown 7 was crewed by West Coast units, including Patrol Boats 753 and 757 from Special Boat Unit 13 and Patrol Boats 775 and 776 from Special Boat Unit 12. On 21 September 1987, Iran Ajr, an Iranian ship converted for use as a minelayer, was attacked. Using night-vision devices, Army gunship crews watched the Iranian vessel lay several mines, then swooped in firing miniguns and rockets. A SEAL team boarded the vessel and quickly seized it. During the attack, five Iranians were killed and 26 were captured. Several Iranian sailors were rescued from the waters of the Persian Gulf after jumping overboard during the attack. After collecting intelligence data the SEALs and EOD scuttled the vessel the following day. In January 1988, Task Force 118 arrived with OH-58D Kiowa Warrior helicopters. Earnest Will ended about five months after the Iran-Iraq ceasefire began in July 1988. Wimbrown 7 soon returned to port, but Prime Chance patrols continued from Hercules until June 1989. Units Ships involved in Prime Chance include: Mobile Sea Bases Hercules and Wimbrown 7, barges leased from an oil company for use by SEALs, EOD, Navy small-boat crews, and Army helicopters Units involved in Prime Chance include: 160th Special Operations Aviation Regiment (Airborne), nicknamed the "Night Stalkers": the army's elite special-operations aviation regiment Task Force 118, a regular army aviation unit flying AH-58D Warrior helicopters whose mast-mounted IR sights helped spot small boats. On 15 January 1991, the unit became 4th Squadron, 17th Cavalry Regiment, and then in 1994, 4th Squadron, 2d Cavalry Regiment. SEAL Team 1 SEAL Team 2 EOD Mobile Unit Five EOD Mobile Unit Six Special Boat Unit 11 Special Boat Unit 12 Special Boat Unit 13 Special Boat Unit 20 Special Boat Unit 24 3rd Battalion 325th Airborne