The M.R.E. / Marshall booster unit was used to test the efficiency of hydraulic roof supports used in mines. It was used from around 1950 to 1985 in Leicestershire's mines.
In the 1950's hydraulic roof supports started to replace the wooden and metal pit props that had been used in mining to provide roof support for hundreds of years.
The first hydraulic pit props worked like the bottle jacks that were used to lift cars and could support up to 20 tons each. These were replaced later in the century by hydraulic chocks which, combined with a steel supporting canopy, provided effective protection from collapse at a continuously advancing coalface.