Sea Base 4 was a sea base in the ocean on planet Earth. It was active in 2084 as part of Sea Base Command. It had several weapons systems including energy tracers.
In 2084 Sea Base 4 was involved in a conflict with the Sea Devils and the Silurians. All of the staff died in the attack. The Sea Devils and Silurians were killed by Hexachromite gas released by the Fifth Doctor. (TV: Warriors of the Deep)