History of the anchor
Until the beginning of the 19th century anchors were of imperfect manufacture, the means of effecting good and efficient welding being absent and the iron poor, whilst the arms, being straight, generally parted at the crown, when weighing from good holding-ground. A clerk in Plymouth Yard, named Pering, in the early part of that century (1813) introduced curved arms; and after 1852 the British admiralty anchor, under the direction of the Board, was supplied to H.M. ships, followed by Lieutenant ("afterwards Captain") Rodger's anchor. Rodger's anchor marked a great departure from the form of previous anchors. The arms were formed in one piece, and were pivoted at the crown on a bolt passing through the forked shank. The points or pees to the palms were blunt. This anchor had an excellent reputation amongst nautical men of that period, and by the committee on anchors, appointed by the British admiralty in 1852, it was placed second only to the anchor of Trotman.
Later came the self-canting and close-stowing Martin anchor, which, passing through successive improvements, became the improved Martin anchor made of forged iron. A projection in the center of the arms works in a recess at the hub of the shank; the vacancies outside the shank are filled by blocks bolted through on each side, and are flush with the side plates, which keep the flukes in position.
The introduction of cast steel in 1894 led to the improved Martin-Adelphi pattern, in which the crown and arms are cast in one, and, with the stock, are made of cast steel, the shank remaining of forged iron. A projection in the crown works in a recess (right image), and is secured in its place by a forged steel pin, fitted with a nut and washer, which passes through the crown and the heel of the shank.
Offshore embedded anchors
Torpedo anchors feature a tubular steel pile, with or without vertical steel fins that are fitted with a conical tip and filled with scrap metal or concrete..  With heights of up to 150m, the anchor becomes completely buried within the seabed from free-fall. Full-scale field tests were performed in water depths of up to 1000m using a 762mm diameter, 12m long torpedo anchor with a dry weight of 400 kN. The torpedo anchor dropped from a height of 30m above the seabed achieved 29m in normally consolidated clay. Subsequent tests with a torpedo anchor, at 240 kN dry weight with an average tip embedment of 20m, resulted in capacities of approximately 4 times the anchor dry weight immediately following installation, which approximately doubled following 10 days of consolidation reaching an ultimate holding capacity of approximately 8 times the anchor dry weight. While the efficiencies are lower than what would be obtained with other sorts of anchor like a drag embedment anchor, this is compensated by the low cost of fabrication and ease of installation. Therefore, a series of torpedo anchors can be deployed for station-keeping of risers and other floating structures