Jonathan_S wrote:Rincewind wrote:Actually you are not quite right. In the Royal Navy the classification is on the basis of role and NOT by size. Destroyers are Air Defence warships and frigates are either Anti-submarine or general purpose. Also, unlike the United States Navy where all ship capabilities are built around the Carrier Battle Group, Royal Navy frigates are intended for autonomous operations.
Some of our frigates have been quite large ships, larger than destroyers
Though as recently as the 50s the RN used frigates for different specialized roles, having the:
Type 41 or Leopard class anti-aircraft defence frigates
Type 61 Salisbury class aircraft direction (AD) (or radar picket) frigates
Type 12 or Whitby-class anti-submarine frigates
It's just that they found all but the specialized anti-submarine designs to be unsatisfactory - partly because of lack of commonality of parts and equipment, multiplying maintenance and supply issues. Anti-submarine effectiveness justifies some unique hardware for quieting, while also being expensive to include on all ships, where as the other uses really don't so a split between ASW and general purpose ships was determined to still make sense.
And I do wonder how much of the decision to make RN destroyers the air defense specialists had to do with the size ship you needed to carry a useful number of the big missiles needed for useful SAM range in the 60s and 70s. Kind of forced into it by default - though IMO it's stretching things to call a 6,200 ton ship a destroyer in 1962; the County-class air defense destroyer having almost twice the displacement of the contemporary USN Charles F. Adams-class guided missile destroyers. It was almost 15 years before the USN built an anti-air destroyer that large.
I think part of the reason was trying to sell it to the politicians. The original designs for air-warfare ships were for cruisers with a displacement up to 17,250 tons & crews of 1,050. This was obviously unaffordable so they came up with a cheaper design based on a conventional gun armed destroyer: (see Rebuilding the Royal Navy by David K Brown & George Moore for the evolution of this design).
Another point is that, as you described by your examples, frigates were originally single role vessels & sloops were general purpose vessels. Then they were faced with a general reduction in the fleet whilst simultaneously having to cater for a commitment to declare seventy frigates for NATO. So general purpose ships were reclassified as frigates & voila, they could meet the commitment.
Ultimately it's all about politics. Look at all the hoops the Navy had to go throw to get the Invincibles built, especially when they were forbidden to call them aircraft carriers; (their original design origins did stem from cruiser studies although it eventually morphed into a through-deck flight deck). Then, when the Soviet Navy began to deploy their first carriers the Thatcher government decided to reclassify the Invincibles as aircraft carriers to make it appear the Royal Navy was stronger than it looked.
As for the point about the Charles F Adams-class DDG's, at the same time the USN was building a series of Frigates; (both gun-armed & guided missile). Ultimately all the gun-armed frigates & one class of guided missile frigates; (the Coontz-class) were reclassified as guided missile destroyers whilst the remainder were classified as guided missile cruisers.
P.S. The Frigates were also described as Destroyer Leaders & they did use the DL/DLG identifier.
P.P.S. If you want another variance if you look at the all the classes based on the US Navy's Spruance-class DD962 hull the Spruances & the Kidds were classed as destroyers & the Ticonderogas were classed as guided missile cruisers. My point? In the Royal Navy the Kidds would have been classed as DDG's but the Spruances would have been classed as frigates: (God knows what they would called the Ticonderogas. Probably cancelled them, more than likely).