The Britannic: She was fitted with all the improvements that were learnt from the Titanic disaster – including better bulkheads that ran all the way to the top deck of the ship. There were waterproof hatches deep in the hull to allow stokers and similar to service the engines bygoing from one waterproof compartment to the next. To cut a long story short, what happened was that by the time the ship was ready, World War II had broken out and she was comandeered as a hospital ship and sent to the Mediterranean. In spite of being painted white with a red cross on her side she was still hit by a torpedo and sank. In spite of having all the improvements, she went down quicker than the Titanic did, although the loss of life was not so great due to the location and the improvement in the number of lifeboats, the latter being another lesson learnt from the Titanic disaster.
The ship had been designed to operate in the cold North Atlantic, so in the Med, not only were the hatches in the bulkheads kept open to assist with air circulation for the stokers, the portholes were actually open too! Consequently, water just flooded in.