Upon entering service in December 1933, the SMERALDO left the shipyard TOSI remaining in Taranto assigned to the “Inspectorate Submarines” which took care of the initial training. As part of this activity, in 1934 the boat completed a cruise in the eastern Mediterranean.
In 1935, the boat was deployed in Messina, first assigned to the 7th Squadron, then in 1936, to the 9th. But in 1937, it was reassigned to the 45th Squadron, 4th Submarine Group, based in Taranto. During the Spanish Civil War, the boat completed a patrol under the command of Lieutenant Commander Mario Canò from August 25th to September 6th, 1937 off Cape Palos, but without obtaining any result.
When Italy entered World War II (June 10th, 1940), the SMERALDO was assigned to the 61st Squadron, 6th Submarine Group based in Tobruk, Libya. From here, under the command of Leiutenant Carlo Todaro (brother of Captain Salvatore Todaro, Gold Medal), the boat left the same day to patrol off Alexandria, 60 miles to the east. In the early hours of the 11th, the SMERALDO sighted a large ship against which it launched a torpedo, failing due to the heavy sea. It is the first torpedo launched by an Italian submarine in World War II. It returned to Tobruk on the 20th.
On July 3rd, the SMERALDO left for the subsequent patrol and on the 7th and 8th was, unwillingly the protagonist for another record; discovered by British antisubmarine units, it underwent the most dramatic bombardment in the whole war with about 200 depth charges. Despite some damage, it escaped, returning to base in Tobruk.
Nevertheless, the damage received (water infiltration through the resistant hull’s rivets, a broken electric motor, just to mention the main ones) was not repairable with the means available in Tobruk, so the boat was sent to Augusta where, from July 15th to December 2nd it remained in the shipyard. It began operating again on December 15th, for a patrol off the Egyptian coast, and since there wasn’t any enemy shipping, on the 22nd it returned to Augusta. The subsequent mission in the waters off Malta began on January 16th, 1941 and it was interrupted soon after when, on the 18th, a serious failure with the batteries forced the boat back to Augusta. During refitting, Lieutenant Carlo Todaro transferred command to Lieutenant (later Lieutenant Commander) Vincenzo D’Amato.
Activity started again on March 15th, this time in the Cerigotto Channel, between mainland Greece and the Island of Crete. On the 16th, the SMERALDO sighted a seven-ship convoy, escorted by a cruiser and several destroyers, but the position was not favorable and could not conduct an attack. It tried again two days later, on the 18th, when it was able to attack a fast enemy unit, but this one, having sighted the submarine, attacked it and was almost able to ram it, forcing it to dive. On the 22nd, the boat returned to Leros where it remained on a temporary assignment.
From this base the SMERALDO left for two more patrols in the area: the fist south of Crete from the 8th to the 16th of April, 1941. The second from May 29th to June 4th, south west of Cape Crios (Crete). Neither patrols produced any results. Anyway, differently from the Atlantic, in the Mediterranean traffic was scant and always heavily escorted. It was hard life for the submarines forced to strenuous patrols and rewarded by very modest results. Later, the boat returned to Augusta for refitting until September 1st. During this period, Lieutenant Commander D’Amato transferred command to the last skipper, Lieutenant Bartolomeo La Penna.
The patrol of the SMERALDO began on September 15th, 1942 when, along with other boats, it was positioned in the Strait of Sicily to form a naval screen against British naval forces. These forces had left Gibraltar between the 8th and the 14th, directed to the western Mediterranean. Specifically, the SMERALDO was assigned a patrol area off the Tunisian coast where the safety routes bypassing the minefields were located. The boat’s return was scheduled for the 26th, but after the departure from Augusta all contacts were lost.
Since in those days and places, after having verified the British documentation, there is no report of any antisubmarine activity, it should be assumed that the submarine was lost following contact with a mine between the 16th and 26th of September, 1941. Up to then, the SMERALDO had completed 15 missions (8 patrols and 7 transfers), for a total of 10,345 miles.