The Argentine navy on Thursday announced that it had downgraded rescue operations for a missing submarine with 44 crew on board to a search for the missing vessel itself. Navy spokesman Capt. Enrique Balbi said authorities could not “give categorical confirmation” that the ARA San Juan’s crew members were dead, but noted it was very unlikely they could have survived since the vessel went missing on Nov. 15. Relatives of those on board had their hopes dashed last week when officials said an apparent explosion had been detected near where the submarine was last seen. Eighteen countries had joined Argentina in searching for the vessel, marking one of the largest maritime search efforts in modern history.