The United States this week reiterated its promise to grant Israel with an extra $429 million to provide missiles and batteries for Iron Dome, boosting the defense system’s capability to defend civilians from rocket attacks – but the Israel Defense Forces doesn’t have enough personnel to man the new deployments.

The announcement came after Israel and the U.S. solved the main disagreements they had over selling the system, designed to intercept and destroy short-range rockets and artillery shells, to other countries. The remaining obstacle is the batteries’ production pace, which appears to be faster than the IDF can train personnel to operate them.

The U.S. conditioned the additional aid, which is not part of annual American defense aid, on manufacturing parts of the battery missiles in U.S. plants. In December 2013, Israel accepted this demand. The agreement was reached at the request of leading members of Congress, who conditioned their support for approving the aid on creating jobs for American workers. According to the agreement, up to 20 percent of the missiles will be produced in the U.S. in the first year, reaching no more than 55 percent in coming years.