The Soviet-designed MiG-21 fighter was used against Pakistani warplanes because the version used by India is a recently upgraded, “capable” aircraft, the commander of the Indian Air Force said.

The MiG-21 made its maiden flight over five decades ago, and has played its part in armed conflicts since the Cuban missile crisis. The latest combat mission for the aircraft was to intercept Pakistani warplanes engaging targets in an Indian-controlled part of Kashmir.

When asked by journalists on Monday why this model was deployed, Indian Air Chief Marshal Birender Singh Dhanoa said it was still a capable aircraft after its latest upgrade.

Bison is the nickname of the MiG-21-93, one of the latest versions of the veteran aircraft made in the 1990s specifically to modernize the Indian Air Force fleet of the fighter jets. The outcome of last week’s engagement, at least as seen from the Indian side, seems to have proven the decision right.

Pakistan, which initially claimed shooting down two Indian fighter jets before reducing the score to one, denies losing any aircraft. It also said it didn’t use US-made F-16s in the mission. According to some reports, doing this would have violated the end-user agreement with the United States. Washington is currently investigating, if such a violation happened.

Dhanoa reiterated that India shot down a Pakistani fighter last week and that the aircraft was an F-16, as evidenced by the debris of an AIM-120 AMRAAM missile shown by New Delhi.

“I don’t know what is the end-user agreement between America and Pakistan. If the end-user agreement was that they will not use it for offensive purposes, then I think they have violated that end-user agreement,” the official said.

The flare-up between India and Pakistan started last week with an Indian air raid on a suspected terrorist camp in Pakistani territory. Islamabad retaliated the next day, attacking targets in the Indian-controlled part of Kashmir. The descriptions of the events provided by both sides conflict on many points, from the effectiveness of the Indian air strike to the claimed loss of the F-16 by Pakistan.