SS Princess Alice was a Thames river steamer which sank after a collision in 1878 with the loss of around 640 lives.

The Princess Alice was first launched in 1865. Originally known as The Bute, she was bought by the London Steamboat Company in 1866. They renamed her the Princess Alice and put her into service on the Thames excursion route.

The trip out was uneventful, and most of the return was also. By 7:40 PM, she was within sight of the North Woolwich Pier, where many passengers were to disembark. This is when she sighted the Bywell Castle.
The Bywell Castle displaced 890 long tons (904 tonnes), much more than the Princess Alice. She usually hauled coal to Africa. At the time, she held no cargo; she had just been repainted at a dry dock and was on her way to pick up a load of coal. She was skippered by Captain Harrison, who was accompanied by an experienced Thames river pilot.
Captain Harrison, on the bridge of the Bywell Castle, observed the Princess Alice coming across his bow, making for the north side of the river. The Bywell Castle set a course to pass astern of her. The captain of the Princess Alice, William Grinsted however, was confused by this and altered her own course. This brought the Princess Alice into the path of the Bywell Castle.
Upon realizing this, the Bywell Castle's captain ordered her engines reversed, but it was too late. The Bywell Castle struck the Princess Alice on the starboard side. The Alice did not stand a chance against a ship that was some four times bigger, and she was sliced in half and sank in four minutes. The passengers were either trapped in the sinking craft, or thrown into the river.

Somewhere between 69 to 170 people were rescued from the river. However the vast majority perished. When the two halves of the Princess Alice were raised, hundreds of passengers were found piled near the exits to the saloon. Many of the victims were never identified due to the extremely heavy pollution of the water. One hundred and twenty of the estimated five hundred and fifty people drowned that day were buried in a mass grave at Woolwich Old Cemetery, Kings Highway, Plumstead. A memorial cross was erected to mark the spot, 'paid for by national sixpenny subscription to which more than 23,000 persons contributed'.