Bethe remained an opponent of ABM systems, and when he heard of the Excalibur effort he arranged a trip to LLNL to grill them on the concept. In a two-day series of meetings in February 1983, Hagelstein managed to convince Bethe the physics was sound. Bethe remained convinced the idea was unlikely to be able to stop a Soviet attack, especially if they designed their systems knowing such a system existed. He soon co-authored a report by the Union of Concerned Scientists outlining objections to the concept, the simplest being that the Soviets could simply overwhelm it.