An unarmed Minuteman 3 intercontinental ballistic missile blasted off early Wednesday on a test flight from California to a target in the Pacific Ocean, but a communications problem forced the launch command to be issued by ground control rather than an airborne launch control system, the Air Force said.

The ICBM roared out of a silo at 6:35 a.m. PDT and its re-entry vehicle reached a target near the Kwajalein Atoll in the Marshall Islands after an approximately 30-minute flight over 4,200 miles of ocean, a base statement said.

The launch command was supposed to have been sent by an E-6B Mercury jet from Offutt Air Force Base, Neb., but a communication issue during the countdown required the command to be sent from Vandenberg control instead, the Air Force said. The E-6B is a four-engine derivative of the Boeing 707 that serves as an airborne command, control and communications platform.

The Air Force said there were also unscheduled countdown holds Wednesday due to bad weather downrange and detection of boats at times in the launch hazard area.

Col. Keith Balts, the 30th Space Wing vice commander, said in a statement that the launch team trains for the types of scenarios it faced Wednesday morning. The range operations were safe and the launch was successful, he said.

Vandenberg regularly tests ICBMs to collect data on the weapons' accuracy and reliability. The Minuteman 3 used in the test had been pulled off alert from its silo near Minot Air Force Base, N.D.

Another Minuteman 3 launch is scheduled July 27 from Vandenberg, located on the coast about 130 miles northwest of Los Angeles.