The First Sea Lord in the British Government, or First space Lord in this situation, is as I said, the equivilant of the Secretary of the Navy in the US,
However the Secretary of the Navy cannot do what the First Sea Lord can, which is replace the men at the top with their own handpicked replacements. Every time the government shifts in Britain, the new FSL can remove any of the commanders of such departments as Buships, Buweps, Personnel, procurement, Operations (Their Equivalent to CNO) or Intelligence. When it is done very badly, a lot of problems can occur. If you have not read the Honor Harrington Series by David Weber, I would suggest reading War of Honor where the inner workings of a very badly run Navy can be seen in glaring detail.