Otago and Taranaki were the only two Otago-class frigates; they differ from the Rothesays that served in the Royal Navy as they were not reconstructed to the Type 12I Leander-class standard with hangar and landing pad for a Westland Wasp anti-submarine helicopter as the main weapon system with torpedoes, depth charges and SS.12/AS.12 missiles to engage fast attack craft and surfaced submarines.

The Rothesay-class was an improved version of the Whitby-class anti-submarine frigate, with nine Rothesays ordered in the 1954–55 shipbuilding programme for the British Royal Navy to supplement the six Whitbys.

[3] In February 1956, New Zealand purchased the Rothesay-class frigate Hastings, which was on order for the Royal Navy, to be renamed Otago and an additional Rothesay, to be called Taranaki.

[4] The New Zealand ships were largely the same as those built for Britain, but had revised internal arrangements,[4] with air conditioning, bunks for the crew rather than hammocks, and cafeteria dining.

Seacat missiles were fitted on the launcher, on the orders of Cpt Tyrrell[21] while Otago was patrolling in French territory waters,[22] mortars, small arms and torpedoes, were also carried.

HMNZS Otago was flying three battle ensigns, officially as an aid to recognition[23] and to signal this was a RNZN operational warship on a political not a protest mission.

The Royal Navy had deployed an RFA tanker and an amphibious landing ship to allow for evacuating the Pitcairn Islands if the French conducted a much larger "megabomb" test but that did not happen.

The objective was to lead a NZ government and world protest against 'illegal' atmospheric testing, demonstrate ability for 'innocent passage' in international waters outside the French territorial 12-mile zone and, while avoiding confrontation, maintain the right to self defence.

On the insistence of the PM, executive and CEO of Foreign Affairs (and possibly their Australian counterparts, who reduced RAN involvement from HMAS Sydney and a destroyer[25] to HMAS Supply a tanker with six 40mm Bofors guns (2 km range) so the RNZN frigates forward in intermediate zone would face any immediate obstruction from the French Navy[26] only the captain and operations officers were informed of the specific instructions - that in certain contingencies French action, fire and attempts to arrest or board the RNZN frigates would be arrested.

[27] Cdr Tyrrell had witnessed the 1957 Operation Grapple hydrogen bomb test at Kiritamati and saw the explosion as puny in comparison and well within safe limits for the crew at the distance.

The NZBC journalists, Shaun Brown and David Barber of New Zealand Press Association on Otago, saw it as an "angry... red fireball" and rising white mushroom cloud.