(Reuters) - An unmanned heavy-lift Delta 4 rocket blasted off from Cape Canaveral Air Force Station on Thursday to put a high-speed broadband communications satellite into orbit for the U.S. military.

The 217-foot(66-metre)-long rocket, manufactured by the Boeing-Lockheed Martin partnership United Launch Alliance, lifted off at 7:38 p.m. EST (0038 GMT Friday).

It was the first of 12 launches planned from Cape Canaveral this year.

Perched atop the Delta 4 booster was a $464-million spacecraft, built by Boeing, called the Wideband Global SATCOM 4. It is designed to relay high-resolution video, imagery, communications and other data at significantly faster rates than predecessor spacecraft.

In addition to linking ground troops and command stations, the satellite will be used to route tracking and data streams from unmanned aerial drones.

"This launch will be another important step in advancing communications capabilities for U.S. warfighters and allies around the world," Boeing Vice President Craig Cooning said in a statement before launch.

The 6.5-tonne satellite is expected to be put into service next year supporting troops in the Middle East and Southwest Asia. It joins three other wideband global spacecraft already in orbit.