Battle of Varna
The start of the use of artillery in the Ottoman Army is not very definite. One of the arguments is that the Ottomans used cannons in the Battle of Kosovo (1389) and Nukap (1396) and most certainly by the 1420s. However the other argument states that field guns entered service shortly after the Battle of Varna (1444) and more certainly used in the Second Battle of Kosovo (1448).