Iran's deep underground nuclear site poses challenge to US airstrikes and Western powers.

The US Air Force posted and then removed rare images of the GBU-57, a powerful bomb designed to penetrate deep into the earth and destroy underground facilities that could be used to enrich uranium. The publication of the photographs comes as Iran is making steady progress in constructing a nuclear facility that is likely beyond the range of the GBU-57, which is considered the US military's last-ditch weapon to take out underground bunkers. The bomb's effectiveness remains unclear, and the B-2 aircraft that can deploy it has been grounded since December.