Hunger

Prison officer Raymond Lohan prepares to leave work; he cleans his bloodied knuckles, checks his car for bombs, puts his uniform on, and ignores his comrades.
Davey Gillen, a new IRA prisoner, arrives; he is categorised as a "non-conforming prisoner" for his refusal to wear the prison uniform. He is sent to his cell naked with only a blanket. His cellmate, Gerry, has smeared the walls with faeces from floor to ceiling as part of the no wash protest. The two men get to know each other and we see them living within the cell. Gerry's girlfriend sneaks a radio in by wrapping it and keeping it in her vagina.
Prison officers forcibly and violently remove the prisoners from their cells and beat them before pinning them down to cut their long hair and beards, grown as part of the no-wash protest. The prisoners resist, Sands spitting into Lohan's face, who responds by punching him in the face and then swings again, only to miss and punch the wall, causing his knuckles to bleed. He cuts Sands' hair and beard; the men throw Sands in the bathtub and scrub him clean before hauling him away again. Lohan is then seen smoking a cigarette, as in the opening scenes, his hand bloodied.
Later, the prisoners are taken out of their cells and given second-hand civilian clothing. The guards are seen snickering as they are handed to the prisoners who respond, after Sands' initial action, by tearing up the clothes and wrecking their cells. For the next interaction with the prisoners, a large number of riot police are seen coming into the prison on a truck. They line up and beat their batons against their shields and scream to scare the prisoners, who are hauled from their cells, then forced to run the gauntlet between the lines of riot police where they are beaten with the batons by at least 10 men at one time. Lohan and several of his colleagues then probe first their anuses and then their mouths, using the same pair of latex gloves for each man. One prisoner head-butts a guard and is beaten brutally by a riot officer. One of the riot officers is seen crying while his colleagues, on the other side of the wall, brutally beat the prisoners with their batons.
Lohan visits his catatonic mother in a retirement home. He is shot in the back of the head by an IRA assassin and dies slumped onto his mother's lap.
Sands meets Father Dominic Moran and discusses the morality of a hunger strike. Sands tells the priest about a trip to Donegal where he and his friends found a foal by a stream that had cut itself on the rocks and broken its back legs. Sands drowned the foal and tells the priest, although he got into trouble, he knew he had done the right thing by ending its suffering. He then says he knows what he is doing and what it will do to him, but he says he will not stand by and do nothing. The rest of the film shows Sands well into his hunger strike, with weeping sores all over his body, kidney failure, low blood pressure, stomach ulcers, and the inability to stand on his own by the end. In the last days, while Sands lies in a bath, a larger orderly comes in to give his usual orderly a break. The larger orderly sits next to the tub and shows Sands his knuckles, which are tattooed with the letters "UDA". Sands tries to stand on his own and eventually does so with all his strength, staring defiantly at the UDA orderly who refuses to help him up, but then he crumbles in a heap on the floor with no strength left to stand. The orderly carries him to his room. Sands' parents stay for the final days, his mother being at his side when Sands dies, 66 days after beginning the strike.
The film explains that Sands was elected to the United Kingdom Parliament as MP for Fermanagh and South Tyrone while he was on strike. Nine other men died with him during the seven-month strike before it was called off. 16 prison officers were killed by paramilitaries throughout the protests depicted in the film. Shortly afterwards, the British government conceded in one form or another to virtually all of the prisoners' five demands despite never officially granting political status.

Question: How many prison officers were killed?
Answer: sixteen