HMS Mirtle was a chalk quarry near Buriton in the South Downs where experiments and steaming out of explosives was done. There were two quarries there. One has since been used as a rubbish landfill site - all filled up with rubbish and grassed over. Here is a comparison shot then and now taken from what I think is around the same spot from the tree line in the background and general lay out of the geography. The other side of the road is another quarry where you can still see sleepers from the narrow gauge railway that accessed the site. The entrance to the site I believe was just down this hill on the left - There was a case of a mine being delivered to Mirtle falling off the back of the lorry on this hill and rolling all the way down. Place was called Mirtle as they were looking for a name starting with MIR for Mine Investigation Range. Here are some more photos from the time - Notice the Army are also present as they often helped the Navy with the recovery operations.