Second Sergeant Hu Enhuai, 19, died during national service training last year after his head was repeatedly held under water as part of a survival course meant to prepare budding commandos in case they are captured in war.
The sentences were handed down Friday by a civilian court.
Lieutenants Divanandhari Ambat Chandrasekharan, 29, and Jeff Ng, 28, received a sentence of nine months' jail each for dunking Hu's head into a tub of water several times and "digging" into his nose so that he could not hold his breath, the Straits Times said.
Captain Pandiaraj Mayandi, 34, who supervised the course in August 2003, was handed a three-month jail sentence for ordering the dunking to be carried out.
Warrant Officer S. Balakrishnan, 45, the commander of the training course and conducting officer on the day of the incident, was sentenced to two months' jail for failing to stop the two officers abusing the trainees.
The four were each handed concurrent jail terms of the same lengths for endangering the life of regular serviceman Captain Ho Wan Huo, 26, who was subjected to similar abuse but survived after eight days in hospital.
While delivering his judgement, District Judge Ng Peng Hong described the training methods as "not only torturous but also inhumane", the paper said.
"The training management plan requires training to be realistic and taken to meet actual battle conditions, but that does not mean safety has to be compromised," the paper quoted Ng as saying.
The family of Second Sergeant Hu was not present in court to hear the judgement but issued a statement through their lawyer, Alfonso Ang.
"The family hopes that the correct lessons have been learnt so that such a criminal act ... will never, ever, be repeated," the statement said.
"The family has suffered much pain over Enhuai's death and they hope to overcome this grief as soon as possible. They now consider the matter closed."
But the case is not yet over. Pandiaraj and Balakrishnan, who were granted bail of 30,000 Singapore dollars (18,400 US), have filed notices of appeal against their conviction and sentences.