[1] A new type of 4.5 inch gun with a longer 55-calibre barrel, it was designed in the 1960s for the Royal Navy's new classes of frigates and destroyers.

The new weapon emphasised reliability and rapid response to fire first round from shutdown state (particularly for defence against missiles) over a high rate of fire, allowing a switch to a lighter, single barrel mounting and ammunition of a one-piece design.

[3] The gun system has a combination of electrical and hydraulic components and the full system penetrates up to three deck levels below the weather deck; deep magazine, gun control room and power room, gunbay and the gunhouse.

[10] This "155mm Third Generation Maritime Fire Support" (155 TMF) would introduce a common gun calibre for the British Army and Royal Navy, helping with ammunition logistics, and encouraging joint Army-Navy development of extended range and precision guided shells.

[11] A £4m contract was awarded to develop a prototype, and firing trials were scheduled for 2009[12] with delivery in 2014,[4] but the project was cancelled in the cuts implemented following the 2010 Strategic Defence and Security Review.

The Type 21 frigate HMS Alacrity used her Mk 8 to sink the Argentine transport ARA Isla de los Estados.