RogerBW's Blog

Several modern European navies have fielded Amphibious Transport Docks, ships designed to transport amphibious forces into harm's way while not themselves being major combatants.

The basic idea could be described as a military ferry: there's a well deck or some other way of loading up landing craft in relative safety, lots of storage space for troops and vehicles, and some sort of command centre. Armament is light, and intended only for self-defence. There will be a helicopter deck, but helicopter operations aren't the ship's primary purpose.

The Dutch and Spanish navies have built minor variants of the same core design, which is more or less the Enforcer platform, though individual ships vary quite a bit. HNLMS Rotterdam displaces 12,750 tonnes, but Johan de Witt (nominally of the same class) displaces 16,800; the Spanish field Galicia and Castilla, each at 13,900 tonnes.

Meanwhile the Royal Navy has Albion and Bulwark, at 19,560 tonnes each. One would think that a bigger ship would be more capable. But:

| Ship                | Bulwark       | Johan de Witt           |
|---------------------+---------------+-------------------------|
| displacement/tonnes | 19,560        | 16,800                  |
| propulsion          | shafts        | podded                  |
| speed/knots         | 18            | 19                      |
| range/nm            | 7,000         | 6,000                   |
| troops              | 405-710       | 555                     |
| vehicles            | 67            | 170                     |
| helicopters         | 2 on deck     | 6 in hangar + 2 on deck |
| boats               | 4 LCU, 4 LCVP | 2 LCU, 4 LCVP           |
| crew                | 325           | 146                     |

We don't know just what's meant by "vehicles" in each case, so there's clearly room for argument there; a tank, even the little BvS 10 Viking APC used by the Royal Marines and the Dutch Korps Mariniers, is bigger than a Land Rover. But what does Bulwark do so differently to take up all that extra tonnage?

Bulwark is full of great wide passages so that troops in combat gear can move around freely; I haven't been aboard Johan de Witt, but the few photos I've seen look pretty similar.

I don't know about construction standards; if Bulwark is built to be a bit more survivable, that might account for the difference. (One might think this would be automatic for any military ship, but obviously not for logistics vessels that aren't expected to fight; on the other hand, the Americans' new Littoral Combat Ships are explicitly designed not to be able to survive major hits, but to be abandoned if they take one, the idea being that with remote vehicles, air assets and long-range weapons they should never have to sail into harm's way themselves. But that's a separate argument made much more cynically by people other than me.)