Jumboised Cimarron/Commencement Bay carriers

[kaiserbill]

Various threads on the usefulness various navies found in light fleet carriers such as the Colossus/Majestic Class (and even escort or cruiser conversion carriers) got me thinking..

The Commencement Bay class were the largest, most capable escort carriers.
These were based on the T3 tanker hull, but were purpose built from the keel up as carriers, instead of being conversions of the T3 hull, like the Sangamon class.

19 were built, and apart from some use as helicopter carriers in the 1950's, they saw little use as they were a little too small for jet aircraft.
They ended up being scrapped early (1960-1970) after being in reserve, with very little mileage on them.

However..whilst their utility to the US navy might have been questionable..what about other navies?

The Cimarron class tankers, the same T3 design, were jumboised from the early 1960's..
This added a new centre section, extending their length by 30 meters, out to over 200 meters.
This implies a waterline length longer than the Colossus class.
The conversions, from what I can gather, were achievable quite smoothly when one considers what was done.
Some of the new mid sections were even subcontracted out for construction to Kawasaki in Japan, and towed to the US for final fitment.
Some jumboised Cimarron class oilers lasted until the 90's/ 2000.

Would a jumboised Commencement Bay Class carrier have been a worthwhile exercise?
You would have to increase installed power naturally to bump up the speed up from the 20 knots, but this would probably have been quite feasible with the process involved in jumboisation.

Not sure about the cost, but if it was worthwhile jumboising the oilers, surely it was at least worth considering doing it to a 19 strong fleet of lightly used carriers?
You'd end up with a carrier slightly larger than the Colossus/Majestic..more hulls, and probably suitable for things like the Grumman Tracker, A-4 Skyhawk, F-11 Super Tiger, ASW helicopters...and useful for all the countries or Allies that did go for the light fleet carriers postwar.

 

[GK Dundas]

Interest idea , not too sure about the practically of it. But interesting.

 

[TomS]

I don't think a simple stretch would have worked -- with the separated machinery spaces in the Commencement Bay class, a plug midships might well impact shaft geometry and that's a whole can of worms to open up.

That said, the USN actually looked at a set of possible modifications to make the CVE-105s into viable CVS for the post-war era, in lieu of the limited number of Essex class CVs. It was a lot.

• angled deck with one of the catapults relocated onto it (cats updated to a pair of H4B/C*)
• elevators relocated to the deck edge
• 30-foot bow extension, blisters, and new Sumner-class boilers and Cleveland-class turbines fitted to get up to 24 knots.

This gives you 18 S2Fs for about $22 million in 1953 dollars, in an era when a new CVE (SCB 43) with up to 30 S2F could have been built for roughly $53 million.

* Possibly replaced by the proposed C-10-3 steam catapult, for even more expense.

 

[kaiserbill]

Interesting.
I had initially wondered about installing the jumboised plug, and putting an angled deck on. A catapult and repositioned elevator too.
So pretty much what was looked at as you mention.
You'd get a carrier a little longer than the Colossus, with about the same beam.

The jumboisation process on the oilers was pretty interesting.

How different machinery wise were the Commencement Bay class to the T3 oilers, and indeed the Sangamon carrier conversions?
They seem to have had a little more power machinery wise to bump up speed from 18 to 20 knots.
Was the machinery separated only in the Commencement Bay class?
Most internet sources only speak of improvements to engineering, which one would expect from a ship built as a carrier instead of a conversion.

Is there any good detailed source on the Commencement Bay class?


Edit: Navypedia has some more info..

 

[Archibald]

Commencement bays... Independance... Saipan... there are so many carriers post-WWII possible what-ifs !
They could have
- supported Seamasters and the SSF
- been turned into massive Regulus / Regulus II cruise missile platforms
- launched Scout or ABM / ASAT rockets (Polaris).
- VSTOL aircrafts later (moar Harriers plus CL-84s)

 

[kaiserbill]

Navypedia has this to say:

"Largest and most successful US-built escort aircraft carriers. The project represented improved Sangamon. Hull repeated the hull of T-3 tanker, but was thoroughly improved and re-arranged; the number of watertight bulkheads has increased. Stern-arranged engine and boiler rooms were stored, but machinery became arranged on en echelon, its power was increased also. The area of a flight deck in comparison with Sangamon was a little moderated, but the hangar became larger.

(fd - 3,726 m², ha - 1,382 m² / 7,365 m³): Flight deck: 152.7 x 24.4 m. Hangar: 65.8 x 21.0 x 5.33 m. There were 2 elevators in the center line (7.7 t, 13.4 x 12.8 m). There was 1 H 2 and 1 H 4C catapults. Aircraft fuel stowage: 700 000 l. "

 

[Archibald]

Escort carrier - Wikipedia

en.wikipedia.org

Of the 151 aircraft carriers built in the U.S. during World War II, 122 were escort carriers, though no examples survive. The Casablanca class was the most numerous class of aircraft carrier, with 50 launched. Second was the Bogue class, with 45 launched.

Often wondered what are the other 29 - that number doesn't fit Essex - Saipan - Independance numbers (24+2+9, should be 35...)

 

[TomS]

How different machinery wise were the Commencement Bay class to the T3 oilers, and indeed the Sangamon carrier conversions?
They seem to have had a little more power machinery wise to bump up speed from 18 to 20 knots.
Was the machinery separated only in the Commencement Bay class?
Most internet sources only speak of improvements to engineering, which one would expect from a ship built as a carrier instead of a conversion.

Is there any good detailed source on the Commencement Bay class?

I believe the Commencement Bay was the only CVE class with separated machinery spaces. I am working from Friedman, who notes the separated machinery, faster elevators, strengthened flight deck (from 14,000 to 17,000 lbs), improved AA battery, and enlarged island. He also notes the elimination of cargo oil and pumps in favor of seawater ballast and improved crew spaces. Compared to the Sangamon, there was also better subdivision, and both the main and hangar decks were strength decks (continuous rather than interrupted.) But even he doesn't have a decent internal arrangement sketch for the class.

 

[TomS]

Escort carrier - Wikipedia

en.wikipedia.org

Of the 151 aircraft carriers built in the U.S. during World War II, 122 were escort carriers, though no examples survive. The Casablanca class was the most numerous class of aircraft carrier, with 50 launched. Second was the Bogue class, with 45 launched.

Often wondered what are the other 29 - that number doesn't fit Essex - Saipan - Independance numbers (24+2+9, should be 35...)

Wiki's numbers are all over the map. Under the Casablanca class it says that a total of 142 aircraft carriers were built, the CVE page says 151, etc. It's probably pointless to even think about -- I'm sure they are using different counting criteria (only ships completed during the war, only ones completed after Dec 7, 1941, etc.)

This site provides probably the most clearly defined count I could find quickly:

Aircraft Carrier Operations During WW2

Aircraft Carrier Operations During WW2

ww2db.com

 

[EwenS]

The jumboization process is described here.

“jumboized” WWII warships

After WWII the US Navy modernized war-built vessels to various degrees for many reasons. Many options were available: new weapons, new radars and sonars, enlarged superstructures, new radios, addin…

wwiiafterwwii.wordpress.com

Note it did not involve the insertion of a “plug” in the hull but rather complete replacement of the whole centrebody with a new 394 foot long section.

So of the original 553 foot long ship, about 250 feet remained to be joined to the new 394 foot mid body, giving a new length of 664 feet. So roughly 273 feet of the original vessel was removed. That means virtually everything from the cofferdam area ahead of the foremost cargo tanks to the pump room compartments between the engine room and the aftermost cargo tanks.

Plans of a Cimarron class here
https://www.hnsa.org/wp-content/uploads/2014/08/ao106.pdf

There is enough detail in the Friedman plan on p180 of his US Carriers book to show the forward boiler and engine rooms sitting where there were cargo tanks in the Cimmaron oiler.

So any “jumboization” of the design would need to be carried out in an entirely different way from the oilers. That would involve a “plug” being inserted somewhere forward of the forward boiler room. How that would have affected hull strength along its length is then the question.

The way the oiler was “jumboized” the new centre section would no doubt have been restressed as part of the design process.

By the way the Casablanca class CVE also had 2 separated machinery compartments. Each compartment was a combined engine and boiler room. Plan here of CVE-90 Thetis Bay

https://www.hnsa.org/wp-content/uploads/2014/08/cve90.pdf

And finally a plan of the Bogue class CVE-53, completed as HMS Puncher in her “as built” configuration, before the RN modifications were made

Modified by Burrards

 

[TomS]

But even he doesn't have a decent internal arrangement sketch for the class.

Derp. He actually does, it's just not in the index.

 

[kaiserbill]

A plug then could probably be inserted just aft of the forward engine room, extending to the cat space forward of the island? Or perhaps to the gas space just aft of the island?
I wonder where the mooted 30 foot hull bow extension TomS mentions was to begin?

Whilst a 30ft bow extension was probably very simple to achieve, I'm not surprised it went nowhere, as 30 feet additional length doesn't really cut it wrt jet fighters.
From practical demonstrations, the Colossus/Majestic class remains the smallest carrier to have routinely operated non-STOVL jet aircraft.

This was why the jumboised Cimarron class piqued my curiosity, as it would have potentially bumped the Commencement Bay class up into that size bracket.

 

[kaiserbill]

Does anyone know if the Grumman Tracker was ever flown off the Commencement Bay class?
Below are pictures of Trackers from VS 25 on the USS Point Cruz.
The Commencement Bay class did fly off the Trackers predecessor, the Grumman Guardian.
The Guardian was the largest single engined piston carrier aircraft to ever see service, and it's dimensions, apart from unfolded wingspan, are basically the same as the Tracker.

The photos are dated January 1955, and June 1955, which was when Point Cruz was still an ASW vessel.

 

[Yellow Palace]

A plug then could probably be inserted just aft of the forward engine room, extending to the cat space forward of the island? Or perhaps to the gas space just aft of the island?

If you're inserting a hull plug, it needs to be done in the parallel midbody of the ship, so would have to be forward of the forward boiler room.

 

[kaiserbill]

A plug then could probably be inserted just aft of the forward engine room, extending to the cat space forward of the island? Or perhaps to the gas space just aft of the island?

If you're inserting a hull plug, it needs to be done in the parallel midbody of the ship, so would have to be forward of the forward boiler room.

Yes, I had considered afterwards the straighter, parallel portion of the hull afterwards.
Forward, you'd be looking at either in line, or just aft of the island..
..but aft I think the forward boiler and engine room in the Commencement Bay class are within that area, as opposed to the aft boiler/engine room, also found in the Cimarron class.
You can get a better idea looking at pictures such as this below, where you can just make out some smoke on the starboard side from the front bolier/engine room.

 

[kaiserbill]

One of the CB (Commencement Bay) class did get some sort of rebuild/development.
The USS Gilbert Islands was converted into AGMR and rechristened as USS Annapolis in the mid 1960's.
As part of her modification, she had her bow rebuilt as a hurricane bow, which is something that would be looked at for the purposes of this alternative history thread.
A Jumboised CB class, with uprated machinery, would require a new angled flight deck, as well as an island.

The USS Annapolis was the longest serving CB class, serving till 1970, and being scrapped in 1979.

 

[TomS]

Does anyone know if the Grumman Tracker was ever flown off the Commencement Bay class?
Below are pictures of Trackers from VS 25 on the USS Point Cruz.
The Commencement Bay class did fly off the Trackers predecessor, the Grumman Guardian.
The Guardian was the largest single engined piston carrier aircraft to ever see service, and it's dimensions, apart from unfolded wingspan, are basically the same as the Tracker.

The photos are dated January 1955, and June 1955, which was when Point Cruz was still an ASW vessel.

Yes, they did. But the ships were too small/slow to operate them all in weather conditions. The proposed mods I mentioned above from Friedman were meant to improve all-weather availability.

 

[kaiserbill]

Yes, they did. But the ships were too small/slow to operate them all in weather conditions. The proposed mods I mentioned above from Friedman were meant to improve all-weather availability.

Did a bit of digging..
Both USS Siboney and USS Badoeng Strait also embarked and operated S-2 Trackers.
Below is a Tracker on USS Badoeng Straits elevator.

 

[Archibald]

We need a meta-thread were we methodically research some scenarios and missions for those 150 (and counting) US carriers, post-1945.

Aircraft carriers	Essex (24) Midway (3)
Light aircraft carriers	Independence (9) Saipan (2)
Escort carriers	Bogue (45) Sangamon (4) Casablanca (50) Commencement Bay (19 or 24)

24+3+9+2 = 38 "fast carriers"
45+4+50+24 = 123 "slow carriers"
Total: 161 carriers.

What would you do with 161 flight decks ?

Me
- P6M Seamaster support ( = Seaplane Striking Force)
- N156N naval LWF, plus Skyraiders and Skyhawks
- Harriers later, Canadair CL-84 (LPH ?)
- Regulus II big cruise missile
- Ryan AQM-34 Firebee drones
- Trackers & choppers for ASW
- Scout or Polaris rockets

 

[kaiserbill]

Most of the escort carriers would only see use as ASW helicopter carriers, or amphibious warfare vessels.

It was the jumboisation of the T3 hull in the Cimarron class which led me to wonder whether the 19 Commencement Bay vessels could see duty in allied nations..akin to the role the Colossus/Majestic class played.

You could get a useful capability from an extended and modified CB vessel operating ASW helicopters, Trackers, A4 Skyhawks, or even perhaps the Grumman Super Tiger had it gone ahead.

 

[Archibald]

In passing, I wonder why didn't the americans sold more Independance class carriers post war. Nine build: one lost, one nuked, two to France, one to Spain - that leaves four carriers. Two of which were only scrapped in 1971.

Plus the two Saipans. Wonder why these two were not sold either.

 

[TomS]

Does anyone know if the Grumman Tracker was ever flown off the Commencement Bay class?
Below are pictures of Trackers from VS 25 on the USS Point Cruz.
The Commencement Bay class did fly off the Trackers predecessor, the Grumman Guardian.
The Guardian was the largest single engined piston carrier aircraft to ever see service, and it's dimensions, apart from unfolded wingspan, are basically the same as the Tracker.

The photos are dated January 1955, and June 1955, which was when Point Cruz was still an ASW vessel.

Yes, they did. But the ships were too small/slow to operate them all in weather conditions. The proposed mods I mentioned above from Friedman were meant to improve all-weather availability.

And it turns out I was only half-right here. Friedman talks about the weather limitations of the CVEs in relation to the AF, not the S2F. The AF needed 22 knots WOD (day) or 26 knots WOD (night). With the CVEs only producing at most 19 knots, they needed to find favorable winds for ops and could not always find them. And the AF was considered too big, so that the air complement was not big enough. The angled deck was easier to land on (which was apparently the main constrain for WOD) and the S2F could serve as both hunter and killer (where the AF required two aircraft, one for each role).

 

[kaiserbill]

In passing, I wonder why didn't the americans sold more Independance class carriers post war. Nine build: one lost, one nuked, two to France, one to Spain - that leaves four carriers. Two of which were only scrapped in 1971.

Plus the two Saipans. Wonder why these two were not sold either.

View attachment 696105

USS Saipan mirrored the CB class USS Gilbert Islands in being converted into an AGMR vessel.
USS Gilbert Islands became AGMR-1 USS Annapolis.
USS Saipan became AGMR-2 USS Arlington.
Both served until about 1970, being scrapped a few years later.

 

[BlackBat242]

USS Saipan CVL-48 served on active duty as an ASW carrier from her initial commissioning in 1946 until 1954, when she became the USN's primary training carrier until decommissioning in 1957 (including time off Korea during that conflict).

She entered shipyard in March 1963 for conversion to a command ship like Wright had become, her conversion was altered in late 1964 to become a communications relay ship, completing that work in 1966.
She was decommissioned in Jan 1970, and scrapped in 1976.


The other Saipan, USS Wright CVL-49, served on active duty as an ASW carrier from her initial commissioning in 1947 until decommissioning in 1956 (including time off Korea during that conflict).

She had been held for future use, and was converted to a Command Ship in 1962-63.
She served in the capacity of the National Emergency Command Post Afloat until decommissioning again in May 1970 and being scrapped 1980.


Of the Independences, outside of those you listed, 2 served on active duty as ASW carriers:
Monterey CVL-26 Sept 1950 - Jan 1956 (scrapped 1971)
Bataan CVL-29 May 1950 - April 1954 (scrapped 1961)
Cabot CVL-28 also served on active duty as ASW carrier Oct 1948 - Jan 1955 before her transfer to Spain in 1967.

Only 2 never saw other use...
Cowpens CVL-25, decommissioned Jan 1947, scrapped 1960
San Jacinto CVL-30, decommissioned March 1947, scrapped 1971

Belleau Wood CVL-24, decommissioned in Jan 1947, was transferred to French Navy in June 1951, and returned to the US for scrapping Sept 1960.
Langley CVL-27, was decommissioned in Feb 1947, transferred to France on 2 June 1951, and returned to US for scrapping in March 1963.


The main reasons no one else bought/leased one are:
1. no desire by anyone the US was willing to let get a carrier,
2. Those the US was willing to see get a carrier got Colossus/Majestic class CVLs - which were bigger & better (except for speed) than the Independences as carriers, and cheaper to operate, needing less upgrading to operate modern aircraft (their enclosed hangars were better for bad weather/heavy seas than the open hangars of the Independences).

The Independences were also a compromised design with stability issues as well as an inefficient internal layout, due to their design as a converted light cruiser (6 of the first 7 were converted on the building ways after being started as light cruisers):
CVL-22 laid down 1 May 1941, conversion started 10 Jan 1942 - 8 months 1 week
CVL-23 laid down 2 June 1941, conversion started 16 Feb 1942 - 8 months 2 weeks
CVL-24 laid down 11 Aug 1941, conversion started 16 Feb 1942 - 5 months
CVL-25 laid down 17 Nov 1941, conversion started 27 Mar 1942 - 4 months 1 week
CVL-26 laid down 29 Dec 1941, conversion started 27 Mar 1942 - 3 months
CVL-28 laid down 16 Mar 1942, conversion started 2 June 1942 - 2 months 2 weeks

The remaining 3 were all built from keel-laying on to the same "conversion" design, and thus had the same limited ability for modernization.


Remember, the Saipan class were designed around the hull & propulsion train of the Baltimore class heavy cruisers... but were otherwise a "clean-sheet" design, not a "conversion" design.

Had the US built more Saipans I could easily see them taking some of the Colossus/Majestic sales, as they would have been very amenable to modernization, but the USN had plans for the 2 they actually had so they were unavailable.