The shell was discovered on Friday evening by workers who were excavating a site off Bell Lane in London Colney.
Homes were evacuated and a 400m cordon was put in place. The shell was moved to nearby playing fields after six initial attempts to detonate it failed.
Residents were allowed home and bomb disposal experts returned on Sunday to detonate the shell successfully.
Most Popular Now | 65,214 people are reading stories on the site right now.";