Deployment ratios and the U.S. Submarine fleet

Submarines, like all military assets, are a scarce resource, especially to commanders who rely on their capabilities. One of the main reasons they're scarce (like everything else!) is that they cost money - a lot of it. So the size of the U.S. Navy's submarine forces has been something that has seen a great deal of debate since the early 1990s, when their then-primary opponent the Soviet submarine fleet picked up their toys and went home.

One measure of the usability of submarines is the 'deployment ratio' - for those likely vanishingly few of you here who don't think about such things, this simply means the ratio between the number of submarines the Navy possesses and the number of submarines that it can maintain forward deployed - i.e. available to commanders - regularly.

In 1999, VAdm Giambastiani, then COMSUBLANT, told a Senate subcommittee that the deployment ratio for SSNs was such that the Navy could maintain 12 boats forward out of a force of 58, with 8 boats unavailable due to refueling or long-term overhaul. So 50:12, or just over 4:1; and the best they could possibly do was 3:1. In his words:

In our Submarine Force of 58 attack submarines, on any given day about 50 are considered operationally ready; in other words ready for sea in a short period of time. However, factoring in crew training and leave, PERSTEMPO and OPTEMPO limits and required maintenance, we provide about 12 forward deployed submarines to the warfighting CINCs. In a major theater war scenario, we can ignore normal operating limits and surge all our operationally ready submarines to defend the nation's interests. But, over the long term, those operations cannot be sustained.

In 2004's "Naval Institute Guide to the Ships and Aircraft of the U.S. Fleet" by Norman Polmar, Polmar says that:

Regardless of the numbers of SSNs, the submarine force must try to increase the ratio of time deployed. While most surface ships have a deployment ratio of roughly 1-in-3, submarines are closer to 1-in-6, i.e., only 9 of about 55 submarines were forward deployed at any given time in 2004.

He cites this number as taken from the remarks of the Director of Naval Nuclear Propulsion at an NSL symposium. According to the Navy, the number of submarines had dropped by three, from 57 to 54 in that timeframe - so either the submarine force availability had dropped a fair amount, or those numbers have some 'give' in them, or both.

What is clear is that attack submarines are less 'available' than other vessels in the fleet. This is in stark contrast to their SSBN cousins, which maintained a much higher availability ratio. Of course, SSBNs have several advantages - they perform much more rigidly scheduled patrol activities, insulated from the demands of combatant commanders, they are designed for long-term independent operation, they are larger, and most importantly, they operate with dual crews. I presented a paper at CNA in 2005 discussing the deployment ratios of submarines, and suggested that the attack submarine force should look to its strategic brethren in this era of falling force size for tools to keep its forces available.

I got pushback at the time from several submariners which broke down into the following categories - mission and training limitations, basing limitations, and technical limitations. These, they told me, were the reasons that the SSN force could not maintain the deployment ratios of the SSBN force. Mission and training limitations reflected the fact that the required mission activities and skill sets of the SSN force were much more widely varied and 'events driven' than the SSBN force, which meant that much more training time as well as less predictable mission requirements meant that the boats would spend much more time preparing for deployments and keeping current. Basing limitations were just that - while the SSBN forces traditionally operated from tenders close to their operating areas, the SSN force needed to transit from US bases to their forward deployment areas, with the exception of a few submarines part-based in Guam. The technical limitations were varied, but the most oft-repeated was that the SSBN is designed with much more modular systems so that maintenance can be carried out via swap-and-depot repair. This allowed the boats to spend less time actually at pier- or tender-side, as replacement consoles and systems could be switched in. This was augmented by the fact that SSNs had much more limited access - anything that couldn't fit through the smaller 36-inch hatch was pretty much limited to on-site repair in cramped quarters, and this, too, increased pier time.

I realize that without better citations, that looks like it could be a straw man. I won't ask you to trust me - I'll instead ask those among us with submarine knowledge to chime in and tell me if this is out of line, because if so, I'd love to know.

I was forcefully reminded of all this a couple of days ago when Galrahn linked to a number of articles from Undersea Warfare concerning the Ohio SSGN conversions. I was struck by the following statement in one article by Lt. Cdmr. Bill Lear:

The SSGN’s deployment cycle leverages the two crew concept and will consist of four separate ten-week operational periods, each one complimented by an overseas voyage repair period and crew exchange. This cycle results in 12 months of forward presence outside of the continental United States followed by a major maintenance period in Kings Bay, Ga. or Bremerton, Wash. The final result will be 2.4 years of annual forward deployed presence by SSGNs.

Given that we have 4 SSGNs, that means the SSGN force is looking forward to achieving a 1.67:1 deployment ratio. Of course, they're using SSBN platforms, along with forward basing - so they've already got some of the advantages listed above. However, the important bit is the types of missions they will be undertaking. To wit, when asked by UW about the challenges facing him as an SSGN CO, Capt. Traub replies that

What has been your biggest challenge as a CO of an SSGN thus far?
Capt. Traub: Actually, there have been two big challenges. The first is maintaining the crew at a high level of proficiency in many more mission areas than a typical SSN or SSBN has while only being on the ship for half of the time. The second has been that this is the first time for many operations we have conducted. For example, during our last underway we conducted the first TOMAHAWK missile launch from an SSGN, the first minefield penetration exercise from an SSGN and the first shallow operations on an SSGN.

In other words, his boat will be performing (or able to perform) a wider variety of missions than an SSN, and will be called upon to do so more frequently as well (given the small size of the SSGN force).

So my takeaway from all of this is that submarine force numbers are possibly not quite as inflexible due to deployment ratios as were so busily being presented as little as three or four years ago. While I'm not saying that we should consider dropping the fleet size down to the theoretical floor of 20 or 21 boats (giving us the 12 deployed boats of 1999 at 2008's deployment ratios) especially since those boats do not share the technical advantages of the Ohios when it comes to deployability, I do look forward with great interest to seeing what the Virginia DR ends up being with ten or twelve boats in the fleet, and wonder if there aren't ways to mod the later 688 boats to garner some of these advantages (other than of course doubling up on crews).