There has been a lot written about the Illustrious class, much of it critical and a lot of it undeserved in my view. With regard to Illustrious, I don't think there is quite such clear cut a link between the 1941 damage to Illustrious and the final speed reduction in 1945 nor to the claims of ongoing vibration problems postwar or to much worse claims of twisted keels etc in both her and Formidable. I don't think anyone has really done a deep enough dive into the archives to discover the full story.
Let me start by saying that no carrier suffered so heavily and from such large bombs as Illustrious did in January 1941 and still stayed afloat. Built to withstand 500lb bombs she was hit by bombs up to 2,200lb as was Formidable. See the damage reports.
HMS Illustrious, January 10, 1941, Damage Report (Bomb & Shell)
Most of the hits were outwith that part of the flight deck covered by 3" armour plate. So there was bound to be heavy damage. The question is how well that was repaired while she was at Norfolk. And how did it affect the ship in future years.
Many ships suffer from vibrations in various parts of their structure. Often they manifest themselves far from the cause. This can usually be resolved while they are on trials. ISTR reading many years ago that the 5 British carriers that used a three shaft layout suffered in various ways. Mostly they go unremarked on. I've linked some relevant articles at the foot of this response about causes. Ark Royal for example from Poolman about her trials:-
"There were some teething troubles. The forty-foot overhang of the flight deck astern and the position of the rudder immediately abaft the centre screw put an unusual strain upon her lightly built structure aft, and it was necessary to stiffen some of the lighter plating."
Most famously the US battleships North Carolina & Washington experienced terrible vibration problems while brand new out of the yards on trials. It took months of trials to resolve with the eventual solution being a new design of propellor with
5 blades for two of her shafts.
There is a comment on the Royal Navy Warship Histories page for Illustrious for 24 May 1940:-
"Final acceptance trials. (Note: Excessive vibration was noted particularly in the Bridge Structure. This problem was never completely resolved during subsequent service.)"
Such was the urgency to get Illustrious to sea that her trials were cut as short as possible (2 days) and she sailed for work up in the Caribbean less than a month later.
It is the only record I've found to date of such a problem that early in her career but it is curious and raises the possibility of an underlying problem even before she was bombed.
As for the stern gland packing failing, this is a regular maintenance item for ships. I've seen articles saying it can need replaced as frequently as every 3 years. And it would appear that there had been plenty of opportunity to address any issues. Illustrious had refits in early 1943 (3.5 months), late 1943 (3 weeks) and autumn 1944 (8 weeks at Durban). Yet by Feb 1945 the problem was so bad the prop had to be removed while at Sydney. Why the sudden deterioration in the space of 4 months? Was removing the centre prop merely a precautionary measure to ensure it wsnt going to be a bigger problem when she was fat from a dock?
I have harboured doubts about the intention to send Illustrious to the Pacific in 1945 in the first place. RN plans for the BPF always revolved around the core of a 4 fleet carrier task force. The only reason I can see for sending Illustrious, given that that prop had to be removed, was due to delays with Formidable. Never much mentioned is the fact that Formidable suffered a major machinery failure (some kind of turbine failure IIRC) after she left the UK at the end of Sept 1944. She then spent 3.5 months at Gibraltar being repaired before continuing her journey east. Had she arrived on schedule Illustrious could have been sent home.
Incidentally, the reduction in Illustrious's speed to 25 knots is not the big issue that it might first appear. Carrier Task Force standard operating procedures saw operations generally carried out at 15-25 knot range. Many reasons for that particularly fuel burn, AS escort limitations to name but two as I've noted previously on other threads.
Now Friedman. Yes she had her centre propellor removed and the shaft locked while at Sydney in Feb 1945 due to a vibration problem. Everyone agrees about that. But just what was the cause of the vibrations leading to the speed reduction to 19 knots?. What Friedman actually says is this:-
"Illustrious suffered Kamikaze damage on 6 April 1945, a bomb-carrying Judy (D4Y3) skidding past her superstructure into the water The only immediate apparent damage was a large hole in the 272 radome forward of her bridge. However, the Kamikaze's bomb exploded underwater near the ship, causing severe shock damage. The outer hull was opened up and some of the frames cracked; Illustrious was limited to 19 knots."
So the speed reduction comes
after the kamikaze strike. The bomb has been variously rated at 1700-2000lb in different publications. In suicide form the D4Y3 could carry 800kg (1,764lb). It exploded about 50 feet from the ship. The extent of the hull damage only became apparent when they put divers down after the ship arrived at Leyte Gulf on 16 April. That was the final nail to end to her wartime career. For comparison, look at the hull damage she suffered while at Malta from a near miss from either an 1,100lb or 2,200lb bomb. If the 1945 damage was comparable then it is small wonder she had a vibration! And she escaped from Malta in 1941 at 20 knots.
And the bomb that caused the Malta damage was only supposed to be 1,100lb. Is it small wonder therefore that her speed was further reduced if damage was on this kind of scale?
And now we come to postwar. She spent 12 months under repair and refit at Rosyth from the end of June 1945. There is a passage in an article refuting many of the comments about Illustrious in an article written by Stuart Slade. It is worth repeating here, but I've provided the links below for anyone wanting to read more.
"Of the British armored carriers, Formidable and Illustrious were write-offs due to war damage. By the end of the war, Illustrious was in very poor condition; her centerline shaft was history due to structural deformation and her machinery was shot.
- Illustrious had been at war since 1940 and Victorious and Formidable since 1941. Naturally, they had been "used" much harder than 1943/44 Essexes which served shorter combat careers (many not more than one operational war deployment). So it is natural for their post-war condition to be poorer than the Essexes.
A more accurate 'tour of duty' comparison would be with the treaty ships Enterprise and Saratoga.
- The unique circumstances of Illustrious's battle damage has already been referred to (but not mentioned by Slade). Her centreline shaft had to be cut away in 1945 to reduce vibrations. Ironically, it was a US solution for severe vibrations in its own warships that was applied in late 1945 to fix Illustrious - a five-bladed propeller was affixed to her repaired centre shaft. Vibrations returned about three years later due to wear on the wing shafts."
As I noted above replacing the stern gland packaging is a regular maintenance item for ships so not necessarily indicative of a hangover from wartime damage.
Slade article
History and Technology - Were Armored Flight Decks on British Carriers Worthwhile? - NavWeaps
Response refuting many of the criticisms raised by Slade
Report:
Another aspect of the Illustrious class that is only rarely touched on is the problems Victorious, which suffered no major hull damage during the war, had with her rudder starting in Aug 1944. From McCart "HMS Victorious 1937-1969":-
"...the Victorious suddenly hoisted 'Not Under Control' balls at the masthead as her rudder had jammed. It was the first indication of a problem which was to stay with her for the rest of her career."
She then immediately spent about 2 weeks at Colombo for "maintenance" followed by a month Nov/Dec in the dry dock at Bombay to try to fix it. She had then been scheduled to have a 7 week period in dry dock at Sydney from mid-Aug 1945 after the operations off Japan. That was to have included fitting a new rudder shipped out from the UK. That refit was cancelled. Instead she carried it home, suffering more rudder problems in heavy weather en route to Colombo. It was finally fitted Oct-Dec 1945 at Devonport as part of the refit she received there.
So the question I have is, was there some kind of design weakness in these 5 carriers (Ark & the 4 Illustrious) around the stern section as a result of choosing a three shaft layout in the first place? Perhaps it was made worse in Illustrious by virtue of her bombing off Malta. But none of it seems to add up to the claims of bent & twisted keels etc. If things had been that bad why hasn't it appeared in official documents that the likes of Hobbs & Friedman can reference. If I've missed something I'd like to hear about it.
It is interesting that both the other great carrier navies, Japan & the USA, came to see the advantage of flight deck armour if not the full blown armoured box hangar on British carriers. The Japanese did come closer with splinter protection to the sides of the hangar and making the flight deck the strength deck in Taiho. On the subject of flight deck armouring all the British, American and Japanese ships fitted with armour on the flight deck restricted it to the areas between the lifts. The advantage that Japan & the USA had was that they could build a bigger ship being free of Treaty limits by the time that thay were laid down.