Missa in tempore belli (English: Mass in Time of War) is a setting of the mass by Joseph Haydn. It is catalogued Mass No. 10 in C major, (H. XXII:9, according to the Hoboken-Verzeichnis catalog). The autographed manuscript contains the title "Missa in tempore belli" in Haydn's handwriting. Haydn composed this mass at Eisenstadt in August 1796. The vocal parts of the mass are performed by four soloists (soprano, alto, tenor and bass) and a four-part choir. The soloists often appear as an ensemble, without arias. Haydn scored the mass for a large orchestra, even adding instruments for a performance in Vienna.

Reference : https://musopen.org/music/3620/franz-joseph-haydn/mass-in-c-major-hobxxii9/