The Flag of Artigas pays homage to José Gervasio Artigas, national hero of Uruguay. It has three horizontal stripes, the top and bottom being blue, and the central one white. On top of them, it has a diagonal red stripe.
The Flag of Artigas is flown alongside the National Flag and the Flag of the Treinta y Tres on government buildings.
Flag of Artigas Wikipedia
The Flag of Artigas, and emblems derived from it, have traditionally been used as the symbols of the Military of Uruguay.
For much of the 20th Century, warships of the Uruguayan Navy flew the Flag of Artigas as the naval jack, until being replaced by another (historical) design in recent years.
The aircraft of the Uruguayan Air Force display the Flag of Artigas on the fins, as well as a circular version of the flag (roundel) on the fuselages and wings.
There is also a different version of the roundel, known as the Artigas' Cockade, which is worn as a cockade on the uniforms of the Military of Uruguay, and also serves as the emblem of the Uruguayan Army. It is likewise based on the Flag of Artigas, but with blue at the centre, surrounded by white then blue, and with the red diagonal stripe overall.
The flag of the Argentine province of Entre Ríos, mostly governed by the Federal Party and Justo José Urquiza between 1842 and 1870, is inspired on the flag of Artigas and looks very similar, except that it has a 9:14 ratio and the blue stripes are much lighter.