What did a Royal Navy mobile wiping unit do?

What was the job of a Royal Navy mobile wiping unit?

It probably performed degaussing work and helped protect ships against magnetic mines.

The designation probably referred to a mobile degaussing function. The unit would service ships rather than operate as a conventional combat formation. Its work reduced the magnetic signature that could trigger a mine. Mobile wiping units therefore supported fleet survival against the magnetic-mine threat without requiring each ship to solve the problem alone.