The cache container is NOT at the given co-ordinates. You need the two (or three) distances given here. This is an opportunity to do a bit of triangulation of your own.
The actual cache container is 20.804km from ROC Groomsport and 20.724km away from John 5:2-4.
Now, anyone who's ever seen a real paper map will immediately recognise that this yields two possible locations.
(Pedants might argue that as the co-ordinates are WGS84, the two points actually yield an infinite number of possibilities which trace an ellipsoid in a plane perpendicular to the surface of the planet and intersecting it at two points. I'm not really entertaining that. You can assume the cache is on the surface of the Earth.)
One way of validating which is the correct point is to employ a third point of origin. ROC Newtownards is 19.912km away from the cache container. The eagle-eyed ones among you will recognise this as a PMO cache. You'll still be able to find the cache even if you're not a Premium Member, but it'll potentially take you two goes.
The entry hatch to the bunker is in the middle of a field, of uncertain ownership, much like any other field. As such, access might well be trespass.
If you attempt access, please ensure you have a caching buddy on the surface at all times.
Above ground, we can see the usual BPI mount, main ventilation shaft, antenna mount and also the combined ventilation shaft / entry point / GZI mount. What's unusual about this one is the slightly rounded concrete top of the entry point. Never seen one like that before.
I've rated the terrain 1 as a wheelchair user could recover the cache. The terrain, if you wish to go to the bunker, is a 2.0. The cache gets a difficulty of 3 because that's how tough some folk might find the puzzle. Others may find it a breeze!
You can check your answers for this puzzle on GeoChecker.com.
If you're appropriately inclined, these folk have an excellent and quite large ROC museum.
The ROC cache series is open to everyone: if you know of an ROC UMP and would like to place a cache there, or have already done so and would like to join the series, then please contact BaseOverApex through Geocaching.com. This is to keep track of the numbers of bunkers which have caches nearby and to help keep tabs on their condition. We'll also give you a piece of text to cut-n-paste into your listing and hopefully the station's correct moniker to add to the cache title. Throughout the UK there are over 1500 ROC UMPs and when this project was started (August 2014) we could only find about 15 with caches. The hope is to grow this very rapidly.