It came less than a decade after an Irish trawler sank after an incident with a British submarine
The fishing boat was subsequently dragged backwards for 1.6km before breaking free.
Confidential Department of Foreign Affairs documents revealed that civil servants felt an agreed settlement between the British Embassy and the trawler skipper involved was preferable to the matters coming before the Irish courts.
A secret department memo dated September 13, 1990, released as part of the State Archive, outlined concerns over the potential embarrassment of British legal action being triggered for the recovery of the towed sonar array.
The incident occurred 40km east of Skerries, Co Dublin at 7.20pm on September 12, 1989 when an Irish trawler, MV Contestor, alerted the Shannon-based Marine Rescue Centre.
The trawler was operating in the Irish Sea and said its nets had snagged on a submerged object.
Initially, the skipper, Sean Daly, said there appeared to be no imminent danger to his vessel and crew.
However, the skipper raised the alarm at 8pm to say his vessel was now being towed backwards.
Ultimately, the trawler was towed backwards for 1.6km before it managed to break free.
An examination of its nets revealed a buoy suspected to be military in origin.
Mr Daly brought the buoy ashore and handed it to the Naval Service.
It determined it was a towed sonar array from a submarine with the markings: “Admiralty Ref - Patrick Engineering Co – Serial No 119 of 1987.”
Irish officials raised serious concerns over the incident with the British authorities as it came less than a decade after an Irish trawler sank after an incident with a British submarine.
"This latest incident will certainly give rise to serious anxiety on the part of fishermen and we ask you to take all possible steps to ensure that there will not be a recurrence," a department note to the British Embassy advised.
Department of Foreign Affairs officials were notified on September 15, 1989 that Mr Daly had commenced legal action for salvage under the Merchant Shipping Act, 1894 – with the buoy being retained by the Irish authorities "until payment is made for salvage".
A department briefing note on September 13, 1989 noted that the area involved is "marked on on Admiralty charts as a submarine exercise area and fishermen are cautioned to keep a lookout for submarine activity".
The towed sonar array unit was subsequently transferred to Clancy Barracks for safekeeping.
However, the following year Irish officials were made aware that Britain had obtained private advice from an Irish lawyer that they could claim "state immunity" – which would prevent salvage being claimed and would force the return of the sonar array.
Irish officials were bemused by the legal concept involved and noted that it had never been tested in Irish law.
Civil servants decided it was best not to give specific advice to the British Embassy but to make it clear that a negotiated settlement was in everyone's best interests.
"I suggest that we reply informally to the Embassy on the line that – the question of state immunity is for the courts to decide and we are not in a position to offer advice on the matter," J Farrell of the Anglo Irish Section wrote on September 13, 1990.
"We would naturally prefer if an agreed settlement could be achieved without the need for litigation."
The memo concluded with the warning that the Department of Foreign Affairs could not interfere as requested by the British Embassy given the statutory obligations on the receiver of wrecks under the Merchant Shipping Act.