The US military has handed down much less severe sentences in similar cases, although civilian courts have been tougher

The 35-year sentence given to Bradley Manning on Wednesday, for passing classified military documents to WikiLeaks, was criticised by many observers as being especially harsh when compared to punishments that have been meted out for similar crimes.

Although prosecutors had demanded he serve at least 60 years, there is a sense among observers that the length of Manning's imprisonment is harsh, especially when compared to the punishments given to other military and government personnel convicted of leaking information or other crimes.

Marine Sergeant Clayton Lonetree

Lonetree, the only marine to have ever been convicted of espionage, was sentenced to 30 years in prison for providing the Soviet KGB with the identities of CIA agents in the 1980s. Lonetree had also handed over the floor plans of US embassies in Moscow and Vienna. His sentence was reduced to 15 years when the secretary of the navy found that the effect of his actions "was minimal". He was released after serving nine.

Army Specialist Albert T Sombolay

In 1991, Sombolay was convicted in a military court of giving a Jordanian intelligence agent information on the build-up for the first Iraq war. He had also passed on documents and samples of US army chemical protection equipment. He was sentenced to 34 years in jail, of which he served only 12.

Michael Peri

Peri, a military electronic warfare systems analyst for the US Army, was convicted of espionage in 1989. He was found to have stolen a portable computer used to store classified military information and handed it to East Germany. Peri pleaded guilty to espionage charges and was sentenced to 30 years in prison – avoiding a life sentence.

The Haditha killings

US marine Frank Wuterich with his lawyers. Photograph: Gregory Bull/AP

The punishment for military personnel convicted of arguably more serious crimes is often less than what Manning faces. In 2005, 24 unarmed Iraqi men, women and children were gunned down by a group of US marines in what became known as the Haditha killings. Charges were filed against eight marines, then dropped against seven. Murder charges against the remaining suspect, Frank Wuterich, were reduced to involuntary manslaughter and aggravated assault. Wuterich struck a deal with military prosecutors and pleaded guilty to one count of negligent dereliction of duty. He was sentenced to forfeit two-thirds of his pay for three months, and a reduction in rank to private.

Aldrich Ames

The US civilian courts have tended to give harsher sentences than their military counterparts. Ames, a 31-year veteran of the CIA, is one of the more famous espionage convicts.

In 1994, he was arrested and accused of spying for the Soviet Union since 1985. Ames was convicted of passing classified information about CIA and FBI "human sources" to the KGB and details of technical operations relating to the Soviet Union during his time in Turkey and Italy. Upon returning to the US, he continued to pass documents to the KGB; the CIA and FBI found their Russian sources were being executed. Ames was sentenced to life in prison without the possibility of parole.

Robert Hanssen

Hanssen, a former FBI agent who was convicted in 2001 of spying for Moscow, was sentenced to 15 consecutive sentences of life in prison without the possibility of parole. He had first provided information to the Soviet Union in 1979 and had continued to divulge secrets – and the identities of agents– throughout the 1980s and 90s. Among Hanssen's crimes was giving up the identities of three KGB agents who were working for the US – two of them were executed. Hanssen was apparently unaware that all three had already been exposed by Ames.

A government transparency advocate, Steven Aftergood of the Federation of American Scientists, said the sentences handed to Ames and Hanssen in civilian court were determined by their being career intelligence officers who had knowingly supplied foreign governments with US secrets over a number of years. In Ames's case, his disclosure led to two men being killed.