Ten hours away from homeland...Bismarck!

There were two U-Boats in the area:
U-556 and U-74

There were several problems that prevented any means to help, one of which, was the U-556 was returning from an Atlanic convoy attack and was empty of torpedoes and low on fuel. The other was the actual location of the Bismark (the British, of course knew the exact location).

The U-556 met the U-74 on the surface during the evening of May 26 to communicte, as the U-556 was having radio problems. U-74 had received orders to engage enemy ships in the area and to retrieve the Bismark's log if possible and was relaying the order to retreive the log to the U-556, but as alredy mentioned, was not able to because of a low fuel situation.

The morning of the 27th, the U-74's sonar reported battle and sinking sounds and investigated, finding British warships in it's sights, but because of heavy seas, was not able to get a firing solution. Wreckage and survivors in life vests were also seen in the periscope.

Sortly after, the British ships left the area and the U-74 surfaced and proceeded to look for survivors. All were dead except for three in a small lifeboat...in spite of the heavy seas, the three were brought aboard and the U-74 continued it's search through the next day but found nothing but dead.

Later on the 28th, the U-74 was ordered to return to Lorient, which incidently came under torpedo attack by a British sub shortly before reaching port.

It's also interesting to note that a Fw200 was spotted flying over the scene at noon on the 27th by the three survivors in the liferaft.

It seems to me, that the Kreigsmarine knew the Bismark was in trouble and it did have assets in the area, such as the U-74. I haven't seen the U-74's mission report, so I don't know when it started it's patrol but as the Bismark was making it's dash back towards France, it would have been an excellent ambush situation for one or more Uboats. This most likely wouldn't have prevented the Stringbags from attacking (depending if/when uboats attacked and their successes) but they may have at least bought the Bismark some time.

U-556's Captain had Ark Royal and Renown in his periscope during Force H's run to the intercept Bismarck, but he was out of torpedoes.

pinehilljoe said:

From what I have read about ADM Tovey , he was like Air Marshall Dowding, doing what was right. Once Bismarck was within air cover, I doubt he would have put KGV into danger from the Luftwaffe. KGV was the only fully operational warship the RN had that could match Bismarck ( PoW still had workers from Cammel Laird on board during the engagement, not all guns were operating) . Given KGV was low on fuel, he would have returned to England, regardless of the Admiralty.

Like Dowding shortly after winning a victory, he was reassigned to a back water billet, in Tovey's case to CinC of the Nore. When Wake-Walker was accused of not be aggressive during the engagement, Tovey defended him and offered to pull down his flag and speak at the inquiry. (From Pursuit by Ludovic Kennedy)

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The Royal navy had contingency plans to refuel KGV in an Irish port. I doubt Tovey would have followed Bismarck to the French coast but he was already technically within Luftwaffe aircover when he sank Bismarck.

Tovey stayed on the job:

Despite these serious differences and although Churchill considered Tovey to be "obstructionist" and attempted to get him sacked, Tovey lasted the full two and a half years of his appointment. At the end of this appointment, when departing Scapa, Tovey was carried to Thurso by HMS Onslow, the later namesake of his notable World War I command.[3]

In June 1943, Tovey became Commander-in-Chief, The Nore, with responsibility for controlling the east coast convoys and organising minesweeping operations. He was promoted to Admiral of the Fleet on 22 October 1943.[26] Other major responsibilities were the organisation of the logistics for the forthcoming Allied invasion of Sicily and the Normandy landings.[7] He was appointed as First and Principal Naval ADC to the King in January 1945.[1]

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(from wikipedia)

Tovey would probably have gone even higher except that the post-war RN contracted rapidly.

I don't there was any debate along those lines, but the navy and airforce were both instructed after it was too late to lend all possible support to save her. uboats in particular were ordered to rush to the scene, and a salvage group was being organized to tr and tow her to port. On the other side of the ledger, the RN was under orders, from Churchill himself, to 'sink the Bismarck" whatever the cost

I am wondering if the Luftwaffe would have been able to help, even if it was within range. There are also training/equipment issues. The Bf 109 F received an artificial horizon and radio compass*, but were the pilots trained to fly over water and perform the mission?

* Not sure about Bf 110.