A U.S.-supplied missile shield to protect Gulf nations against Iranian attacks will take years to complete, requiring a step-up in regional trust, more U.S. sales of sensitive weapons, and intensive U.S. training to avoid mishaps in the volatile region.

A renewed joint commitment to build the regional defense system was one of the few firm outcomes of Thursday’s Camp David summit between President Barack Obama and Gulf allies, which were seeking fresh U.S. defense pledges ahead of a possible nuclear deal they fear will empower arch-rival Iran.

Past efforts have stalled due to tension and mistrust within the six-nation Gulf Cooperation Council (GCC) but U.S. and Gulf officials say the time is now ripe to push ahead as Arab nations mount more joint military missions. […]