A bunker tanker crew allegedly sank their vessel after it was intercepted with three tonnes of cocaine on board.
The incident occurred off Ribadeo, north-western Spain, police said on Wednesday.
Police worked with customs officials and the navy to raid the 846-dwt Nehir (built 2015).
Footage released by the Guardia Civil shows officers boarding the vessel, followed by shots of it partially submerged, before the tanker sinks beneath the waves.
Police said traffickers had planned to move the drugs on to smaller vessels off Galicia, for onward distribution to other European countries.
An investigation began in May 2020, the Euro Weekly News paper reported. Officials had been tracking a gang from Pontevedra province.
When officers realised weather conditions meant the ship would not be able to transfer the contraband to smaller boats, they decided to move in.
Tanker flooded
When the crew saw what was happening, they allegedly flooded the Turkish-built vessel, which sank in two hours, but not before police had recovered the drugs and arrested the men on board.
Spain Journal reported that nine seafarers from Georgia and Turkey were held.
Equasis lists the manager as Salah Ali M Elhiblu of Tripoli, Libya, which could not be contacted.
The last AIS signal from the tanker shows it docked in Morocco on 15 January.
The Nehir has been inspected twice by port state control officials, with neither occasion resulting in a detention.
VesselsValue assesses the ship as worth $5.6m.
Classification certification was withdrawn by Bureau Veritas in 2019.
The tanker was then classed by Turk Loydu, but this was suspended last December for "non-compliance with conditions of class/recommendations", Equasis records show.
