Complex sentence: From June 1915, the regular intelligence reports of ship positions were no longer passed to all flag officers, only to Jellicoe, who was the only person to receive accurate charts of German minefields prepared from Room 40 information.
Split into simpler sentences: From June 1915 the regular intelligence reports of ship positions ceased to be passed to all flag officers, but only to Jellicoe himself. Similarly, he was the only person to receive accurate charts of German minefields prepared from Room 40 information.