various sizes of shells were tested, but it was found that only the largest shells had a useful incendiary effect. experiments were carried out in 1859 using the aged, redundant frigate hms "undaunted" as a target. the first three shells were ineffectual, but after the fourth and fifth more had been fired, a fire had been started on "undaunted's" lower deck that could not be put out with her fire fighting equipment. the ship was finally sunk with conventional shells.