At least 16 People's Liberation Army major generals have been taken away for investigation in relation to graft cases involving their former superiors, according to sources close to the military. Two independent sources close to the PLA told the South China Morning Post that most of the officers were either secretaries or relatives of former military commanders or senior officers. One of those taken away was Major General Guo Zhenggang, son of Guo Boxiong, a former vice-chairman of the powerful Central Military Commission, a Shanghai-based retired senior colonel said. Another was Zhu Heping, a former secretary to late general Zhang Wannian, another former CMC vice-chairman who died in Beijing on January 15, the source said. Guo Zhenggang, 45, was promoted to deputy political commissar of the Zhejiang Military District with the rank of major general in January, Zhejiang Television reported at the time. Rumours that he was being investigated surfaced last month. The investigation of Guo has raised questions about whether his father will also come under the spotlight in the investigation of another former CMC vice-chairman, Xu Caihou. Xu, 71, has been investigated for bribery since last March and was expelled from the Communist Party in June. He is the most senior military figure to be implicated since President Xi Jinping launched his anti-graft drive after taking control of the Communist Party and the military in 2012. Military experts said Guo Boxiong would almost certainly be scrutinised because he was Xu's superior during his 10 years as CMC vice-chairman. Two former subordinates of Xu and Guo Boxiong were also investigated recently, the retired senior colonel said. They are Wang Aiguo, a former head of the joint logistics department at the Shenyang Military Command, which was Xu's powerbase, and Zhan Guoqiao, who held the same post at the Lanzhou Military Command, Guo's powerbase. Another source close to the Guangzhou Military Command confirmed the military region's joint logistics deputy head, Chen Jianfeng, and air force logistics chief Wang Sheng were detained early in January due to their involvement with Lieutenant General Gu Junshan, who was taken into custody in January 2013, and is accused of amassing a personal fortune while deputy logistics chief of the PLA. Gu, a top ally of Xu, was charged with bribery and embezzlement last year. Early reports said Gu was suspected of selling hundreds of senior military positions. It is believed he took bribes worth 600 million yuan (HK$754 million) as part of a greater 30 billion yuan scam. Some of the other major generals detained were only promoted late last year or earlier this year. Zhang Dongshui was taken away on January 7, just 13 days after he was promoted to deputy political commissar of the Second Artillery Corps - which is in charge of China's intercontinental ballistic missiles - the retired senior colonel said. Party leaders say nepotism and promotions secured through bribes have seriously undermined the military's efficiency and combat readiness. The massive crackdown indicated Xi was willing to step in to eradicate the legacy of disgraced top officials.