But the defense officials who received the briefing were told that using conventional bombs, even as part of a wider strike package of several GBU-57s, would not penetrate deep enough underground and that it would only do enough damage to collapse tunnels and bury it under rubble.
Those in the briefing heard that completely destroying Fordow, which Israeli intelligence estimates to go down as far as 300ft (90 metres), would require the US to soften the ground with conventional bombs and then ultimately drop a tactical nuclear bomb from a B2 bomber to wipe out the entire facility, a scenario Trump is not considering.
The assessments were made by the Defense Threat Reduction Agency (DTRA), a component of the defense department that tested the GBU-57, as it reviewed the limitations of US military ordinance against a number of underground facilities.
https://www.theguardian.com/world/2025/jun/19/trump-caution-on-iran-strike-linked-to-doubts-over-bunker-buster-bomb-officials-say