Army of the Danube order of battle

Jean-Baptiste Jourdan received command of the Army of Observation in September 1798, from its temporary commander, Pierre Marie Barthélemy Ferino. From October to December, he assessed its condition. By 27 February 1799 Moreau had drawn together his general staff and laid out his operational plan for a Danube campaign.[7]

The Advance Guard crossed the Rhine River at Kehl, and marched to the northeast. François Joseph Lefebvre was indisposed—suffering from ringworm—and Jourdan had appointed General of Division Dominique Vandamme to direct the march. Vandamme had been lobbying with Jourdan for a larger and more important command but, given the claims of other officers, this was the best Jourdan could do for him. Vandamme led the Advance Guard through the mountains via Freudenstadt. On 5 March, Lefebvre returned to his command.[10] Within a week, part of the advance guard broke off from the main body and, under command of Vandamme, moved to Stuttgart, to investigate the rumored presence of Habsburg units.[11]

The Division crossed the Rhine River at Hüningen near Basel, Switzerland, and marched in two columns eastward. The right column, commanded by Jean Victor Tharreau, moved along the northern shoreline of the Rhine. The left column, commanded by Jean-Baptiste Jacopin, moved at the northernmost rim of the river valley. From Switzerland, Masséna sent a Demi-brigade of the Army of Helvetia to secure Schaffhausen, part of the Swiss cantons that lie north of the Rhine river. In holding Schaffhausen, Masséna insured the passage of Ferino's forward units.[18] Ferino's orders were to proceed from Schaffhausen along the north shore of Lake Constance, also called the Bodensee. His left flank was to remain in contact with the II. Division, to prevent the Austrians from piercing the army's forward line. His advance units were to proceed as far as the Imperial Abbey of Salem. From there, he was instructed to prevent any Austrian reinforcements from Switzerland joining with Archduke Charles, whom Jourdan expected to move across the Iller river near Augsburg, and advance into Swabia.[19]

The Division followed the Advance Guard across the Rhine, also at Kehl. As it approached the mountains, II. Division followed the river valleys east of Freudenstadt.[24] At the Battle of Ostrach, II. Division took position behind François Joseph Lefebvre's Advance Guard, on the slope below Pfullendorf. At the Battle of Stockach, Souham's Division, positioned in the center, was to coordinate a simultaneous assault with Ferino's I. Division on the Austrian left flank.[25]

The Third Division and the Reserve also crossed at Kehl, and then divided into two columns, III. Division traveling through the Black Forest via Oberkirch, and the Reserve, with most of the artillery park, via the valleys at Freiburg im Breisgau, where the horses would find more forage, and then over the mountains past the Titisee to Löffingen and Hüfingen.[24] At the Battle of Ostrach, after more than 15 hours of general engagement, the Austrians flanked the III. Division's left wing and pressed the entire Division back to the Pfullendorf heights.[30] At the Battle of Stockach, Saint-Cyr and Vandamme were to execute simultaneous attacks on the Austrian right flank, Saint-Cyr on the front and Vandamme from the rear; the attacks failed when Archduke Charles moved support troops from the left flank.[31]

The Reserve crossed the river at Kehl, swung south toward Freiburg im Breisgau, and crossed the mountains at Neustadt, to Loffingen, Bruhlingen and Hüfingen.[24] At the Battle of Ostrach, the Reserve remained in the northern outskirts of Pfullendorf and did not participate in the battle except in small groups. When Jourdan decided to withdraw, d'Hautpoul's cavalry moved to the west first, to secure bridges and the east–west roads.[35] At the battle of Stockach, the Reserve was slow to support of Ferino's I. Division, which had run out of ammunition; when a cavalry charged failed to materialize, the Austrians acquired the upper hand.[36] Jourdan later charged d'Hautpoul with dereliction.[37] After the Stockach engagement, most of the Reserve withdrew to the west side of the Black Forest, where the horses could find forage,[24] but by late April, the Reserve had joined with the André Masséna's Army of Helvetia outside of Zürich; d'Hautpoul joined them in July after he was cleared by a Courts-martial in Strasbourg.[37]

Command: Jean Ambroise Baston de Lariboisière[40]

• Cannons: 33 four-pounders; 21 eight-pounders; and seven 12-pounders[16]
• Howitzers: 19[16]
• Personnel (effective strength): 1,329 non-commissioned officers and cannoneers; 60 officers; Total 1,389[41]