NEW DELHI: Presenting a sobering account of long-term as well as immediate challenges, senior IAF and Army brass told a parliamentary committee that while India’s window to catch up with China’s defence modernization thrust could close by 2017 or earlier, stocks of certain types of tank munitions are down to four days of reserves.Responding to queries posed by members of Parliament’s standing committee on defence, IAF vicechief Air Marshal Kishan Nohwar said the asymmetry between India and China was widening with Beijing’s aggressive war doctrine powering a rapid expansion of its military . While he said India would need to be proactive to prevent lagging behind China in terms of its preparedness , Army vice-chief Lt Gen S K Singh told MPs that there was a shortfall with regard to certain tank ammunition due to an Israeli firm being blacklisted, but the situation was not too worrisome as sufficient stocks were available with regard to most weapon systems.Questions on tank ammunition rose from the leaked letter Army chief Gen V K Singh wrote to Prime Minister Manmohan Singh that referred to serious gaps in India’s defence preparedness. In view of evidence presented to the committee on Monday, chiefs of the three Services are expected to brief the panel on April 20.On the controversy over the Tatra trucks, defence secretary Shashikant Sharma said the ministry had written to the Czech suppliers in February seeking to deal with it directly. However, the firm said the dealing should be through its London office, run by businessman Ravi Rishi who was questioned by the CBI last week.Pointing to difficulties in changing the trucks, officials said the vehicles were the platform for India’s missile systems and could not be replaced at a short notice while responding to queries from Majlis-e-Ittehadul MuslimeenMP Asaduddin Owaissi, Congress MP Manish Tewari, Akali MP Naresh Gujral and committee chair Satpal Maharaj.Sources said several questions on defence preparedness were asked about China in the context of a two-front war.The Army Vicechief explained the shortage of tank ammunition was due to an Israeli firm being blacklisted and that India’s requirements were being sourced from Russia. He said the procurement process is being accelerated.On the acquisition of trainers for the air force, the panel was told that while there were delays, the order process was in an advanced stage and could be concluded in May. The need for trainers would be all the more acute as India begins inducting the 126 Rafael fighters it has decided to purchase in order to boost its air power.The IAF Vice-chief said lack of trainers meant that trainees were being able to complete just 25 hours of flying in their first year instead of 150. On the Tatra trucks, the committee was also told the vehicles had not been found wanting and that both Bharat Earth Movers Limited ( BEML ) and Defence Research and Development Organization (DRDO) had given the vehicles a clean chit.