ATAGS, the indigenous howitzer

Context

In a first, an indigenously developed howitzer gun, ATAG, became part of the 21-gun salute during the Independence Day ceremony at the Red Fort.

About

Advanced Towed Artillery Gun System (ATAGS) howitzer:

The Advanced Towed Artillery Gun System (ATAGS) howitzer is the first in the world to have a range of 45 km. It's self-propelled and can be towed easily.
The ATAGS is an indigenous 155 mm x 52 calibre howitzer gun developed by the Defence Research and Development Organisation (DRDO) with its Pune-based facility Armament Research and Development Establishment (ARDE) being the nodal agency.
The ATAGS project was started in 2013 by DRDO to replace older guns in service in the Indian Army with a modern 155 mm artillery gun.
A howitzer is an umbrella term for a category of long-range artillery guns.

The 21-gun salute tradition

When the National Anthem is played by the Military Band after the unfurling of the Tricolour at the Red Fort by the Prime Minister, a 21-volley gun salute is fired by a ceremonial battery from an artillery regiment.
The tradition of gun salutes originates from the Western navies where guns from the ports and those from incoming ships used to be fired in a particular manner to convey that there was no belligerent intention.
This tradition was carried forward as a way of paying respects or for according official welcome to the Crown, royals, military commanders and heads of states.
India inherited the tradition from the British rulers who had gun salutes comprising 101 volleys, 31 volleys and 21 volleys, and so on depending on the hierarchy.
In India, artillery gun salutes are fired on the Republic Day, the Independence Day and also at the time of oath taking ceremony of the President, among other occasions.