Destined to Cuba, he enlisted to join the expeditionary division led by General Prim in Mexico in 1862, although he ended up staying in Cuba. He was later destined to Santo Domingo, and took part in the attack and occupation of Santiago de los Caballeros, retreat from Puerto Plata, and military operations in San Cristóbal, Baní and Azúa, assault and defence of Monte Christi and other, earning the rank of captain. He worked as lecturer of Geometry and Topography at the Havana Military Academy, and, when the broke out, kickstarting the deadly Cuban campaign, he mobilized a small force of volunteers under the name of "Primera Guerrilla Volante". At the helm of said force, Cassola took part in many military operations, including La Mercedes, Santa Gertrudis, Sancti Spíritus or Meloncitos, until falling ill at the vanguard line of the Trocha from Morón to Júcaro. He then returned to the mainland in December 1871, with the rank of Lieutenant Colonel and with a red plaque of Military Merit.