Within the last month three different survey vessels have been seen near Thames shipwreck SS Richard Montgomery off Kent, UK

American Liberty ship SS Montgomery sank in 1944, with 1400 tonnes of explosives onboard 1.5 miles north of Sheerness.

It's the UK's most dangerous and monitored shipwreck under 24-hour radar and visual surveillance.

Vessel Thames Guardian was seen undertaking multiple surveys today (November 7 - and also November 3 & October 30) including: a multibeam sonar survey, gradiometer survey and chirp survey around the wreck and surrounding areas.

A chirp survey is used to detect unexploded ordnance.

Clinton Marine's Northern Wind was seen surveying October 18, and their vessel Lode was seen October 16.

Normally only one sonar survey of the wreck is undertaken each year by a single survey vessel to assess its condition.

The dramatic increase in survey activity is due to a problem encountered by the UK Government's plans to cut-off the shipwrecks three masts last year.

Unidentified objects were found on the seabed in areas where a platform would need to be installed for the mast cutting - which meant the work has had to be postponed - to allow officials to gain more information and determine the safest way to proceed.