Olpæ (Peloponnesian War). Fought 426 B.C., between a small Athenian force, under Demosthenes, and a force of Ambraciots, with 3,000 Spartan hoplites, under Eurylochus. Demosthenes gained a complete victory, by means of an ambuscade, and Eurylochus was slain. Oltenitza (Crimean War). Fought 1853, when a Turkish army, superior in numbers, under Omar Pasha, totally defeated the Russian army which had invaded the Danubian Principalities. Omdurman (Soudan Campaigns). Fought September 2, 1898, between the British and Egyptians, 23,000 strong, under Sir Herbert Kitchener, and 50,000 Dervishes, under the Khalifa. The Dervishes attacked the British zareba, and were repulsed with heavy loss. Kitchener then advanced, to drive the enemy before him into Omdurman, and capture the place. In the course of the operation, however, the Egyptian Brigade on the British right, under General Macdonald, became isolated, and was attacked in front by the centre of the Dervish army, while his flank and rear were threatened by the Dervish left, which had not previously been engaged. The position was critical, but through the extreme steadiness of the Soudanese, who changed front under heavy fire, the attack was repulsed. The British and Egyptian losses were 500 killed and wounded. The Dervishes lost about 15,000. Onao (Indian Mutiny). Fought July 28, 1857, between Havelock’s relieving force, 1,500 strong, and the rebels, who occupied a strong position near Onao, so protected on the flanks that a frontal attack was necessary. This was successful, and after the town had been passed, a further attack by the mutineers was repulsed, with a loss of 300 men and 15 guns. Onessant. Fought July 27, 1778, between 30 British ships of the line, under Admiral Keppel, and a French squadron of equal force, under the Comte d’Estaing. After a fight which lasted throughout the day, the two fleets drew off to repair damages, neither side having lost a ship. Oondwa Nullah. Fought September, 1763, when 3,000 British and native troops, under Major Adams, carried by storm the entrenchments and the fort held by Mir Cossim’s army of 60,000 men with 100 guns. Mir Cossim fled and his army was entirely dispersed. Ooscata. Fought August 23, 1768, when the camp of the Mahratta contingent, under Morari Rao, forming a part of Colonel Donald Campbell’s column, was attacked by a detachment of Hyder Ali’s army. The Mahrattas repulsed the Mysore cavalry with a loss of about 300, at a cost to themselves of 18 only. Opequan (American Civil War).