Seven men, including two who were charged, will face 'no further action' following an incident off the Isle of Wight aboard an oil tanker in October 2019.
On Sunday 25 October, a group of people who were not part of the crew, were found on the Nave Andromeda.
Hampshire Police said the group "made verbal threats towards the crew" but that there had been no reports of any injuries.
All seven were detained under Border Force powers.
Two of the men, Matthew John Okorie, 25 and Sunday Sylvester, 22, had been charged with an offence relating to conduct endangering ships under S.58 Merchant Shipping Act 1995.
However the Crown Prosecution Service has decided not to take further action after additional evidence came to light as part of the investigation.
Senior District Crown Prosecutor, Sophie Stevens, said: “The CPS has a duty to keep all cases under continuous review and after additional maritime expert evidence came to light, we concluded there was no longer a realistic prospect of conviction and discontinued the case.”
The other five men, who were arrested on suspicion of seizing or exercising control of a ship by use of threats or force, remained on police bail until 25 January 2021.
They will also now face no further action in relation to the Hampshire Constabulary led investigation. They will remain detained under immigration powers in accordance with published processes.