In Service - in maintenace - in training - where does it come from?
 

It seems to be taken for granted that military ops (especially ships) work on the principal of a third of units are available, a third in maintenance and a third working-up/training

IIRC this first came out the USN Carrier Air Wing system but it seems to be rife everywhere now

Is it based on any hard evidence or is it just a handy way of reducing costs of operations????

HH, 2/3 in commission seems pretty good to me.

It sounds sensible although a third of an aircraft carrier just doesn't float:E

It does explain though why you only get two sets of keys with a car.

It was the USN Carrier Squadron rotations where I first saw it mentioned a few years back- it does seem a bit odd when commercial ships and aircraft are available and working 90%+ of the time tho'..............

HH, to take the cruise ship case. True they probably do 345 days per year but although large and complex have more space and less electronic complexity.

Refits may take 2-3 weeks but I expect the additional cost of such rapid maintenance is offset by the quicker return to comment service and profit.

Then a crew of over 1,000 can absorb a new personnel more easily. On a typical 8 month contract it means a crew may be completely replaced in 2 years. Greater complexity and smaller crews mean RN crews need to train and learn more complex skills. Also a Naval ship does not work in isolation. You can't afford to send ad hoc crews out on operations as other Navies have discovered.

I think the 'rule of thirds' goes back a longer way than might seem.

As long ago as 1960, when I was toying with the idea of joining the RN to fly, I was told that the Navy worked on a 33% attrition in aircraft during normal ops/training.

I was reminded recently when reading a book about carrier operations, how there was an elaborate replacement/replenishment system, which involved smaller carriers 'feeding' replacements to the fast fleet carriers. Whilst that was war, there was obviously careful planning for managing large numbers of aircraft to ensure the front line was sustained.

O-D

These figures (or targets) were set in the Permanent Long Term Costings Instructions - (mid-80s terminology when I used them). They determined just about everything that cost money. I can't speak directly for ships, but one was allowed to assume 14% of aircraft in the 'repair pool' at any given time (excluding a/c in SBM/SUM). Aircraft and ships were directly related, as the latter required aircraft, so a similar rule must have applied. As we only had 3 CVS, that would be rounded up to 33%. If aircraft rose above 14%, the Admiral would wander down from the 5th floor and ask the question. One assumes that's why MoD needs so many Stars nowadays!

At an equipment level, individual staff officers (now called Requirements Managers) applied (by hand, no computers then) a simple formula called STOCKCAL, which set similar targets for 1st and 2nd Line Recovery rates (10 and 80% respectively). Rule of thumb was, if R2 fell to 50%, robbery was inevitable. If you didn't get this right, you were summoned to the 5th floor. In 1988, as a savings measure, this became 8 and 68%, which left the RM less leeway and robbery more likely. It would seem this is even lower now, although probably not in the permanent instructions. By the way, these instructions were what set out the Requirement Manager's unique authority to use engineering judgement to overrule annual (not permanent) LTC instructions.

hanks Tuc

Interesting how an Admin "setting" has such a significant and long-term impact on capability. Explains a lot

I have been told some time ago that in the days of an RN Aircraft Carrier going on a 18 month, round the world, deployment, they would expect to lose the equivalent of a squadron of aircraft! Is this true?

Aaron.

Aaron Do you mean attrition, or just unserviceable and having to wait until return to port? The annual Instructions, from which the 2nd and 3rd Order Assumptions were derived, set out the latest attrition forecast, based on historical data. I do recall that it was fairly steady in the mid-80s, and the sudden jump from a Lynx loss every 40,000 flying hours, to 30,000, caused ructions. This was about the time 'Sonics Lynx' was being mooted, and it was assumed someone had tweaked the figure in anticipation of the new role. Engines will probably know more, but I know there was a large initial peak in SHAR attrition due to outriggers hitting the ramp. But that settled down.

tucumseh
 

The story I heard was that it was an attrition rate due to accidents and mishaps whilst at sea.


Aaron.

Aaron, on the USN side, numbers in that range predated the implementation of the NATOPS methodology, so 1950's and early 1960's, I'd offer that you would expect that if you did in fact deploy for 18 months. But even by that time, the rotation cycle was typically less than 18 months port-to-port. I seem to recall that Yankee Station rotations were not 12 months continuous, but I'll need to defer to those as were actually on task in that time for their details.

As to the current "one in training, one on task, on in refit" that was a Cold War Optempo intended to deal with the "forever" nature of the Cold War. (It was also aimed at reducing loss of service personnel by leaving/not re enlisting, when 8-10 month deployments were common). I saw that first hand in the early 80's and watched things change over about a decade.