On 11 June 1940, Italy declared war on France and Great Britain. As early as April 1940, Mussolini issued a directive to his commanders to prepare for war ordering measures for offensive action in the Mediterranean against allied naval assets, while keeping a defensive posture in Libya and East Africa.
The swift success of the Germans caused Mussolini to inform his commanders on 5 June that war would be declared on the 10th (to participate in the spoils of war).

Since Great Britain controlled access to the Mediterranean through the Suez Canal and Gibraltar, they blocked the Mediterranean Sea to the Italians. One-third of the Italian merchant fleet (1.2 Million tons) was operating outside of the Mediterranean and was lost because the ships had no way to enter the Mediterranean. These ships were scuttled to prevent capture, were captured by the British, were interned in neutral ports, or reached Italian-controlled Eritrea where they were safe for a while, although they were incapable of leaving port. Had the Italians waited one month to declare war, they would have recuperated over 80% of this shipping. This was an unforgivable mistake on the part of both Mussolini, and his military commanders.

In addition, Italy could not import fuel (except from Ploesti, Romania. But once the Germans entered into this country, Italy was relegated) so it had to make do with its reserves (they estimated they had enough fuel and ordinance to last 6 months for their air force).

While the blockade forced Germany to be bold and take the initiative while supplies last, the Italians initially became utterly timid and carried out minimal operations despite favorable conditions. For instance, their air force was 3.5 greater than the combined strength of GB and France in the Mediterranean but their ineffective intelligence service reported that they had a 3:2 numerical disadvantage.

Italy deployed 507 fighters and 815 bombers of modern types in front-line units (excluding reserves) on 11 June. The RAF deployed only 75 fighters and 96 bombers in the Mediterranean. The size of the Italian air force was significant even when comparing it with the strength in the British Isles. The British had 895 fighters in Fighter Command and 467 bombers in Bomber Command (plus 524 a/c in Coastal Command) excluding reserves.

Once France was knocked out, Malta became very vulnerable to a maritime invasion, but the Italians limited themselves to bombing the island with insufficient forces and using poor tactics.

Later, the Italians attempted bolder moves invading British Somaliland, Egypt, and Greece, but they failed every time. When the Germans invaded Crete, the Italians had the opportunity to turn the war in their favor, thanks to the trashing the Luftwaffe delivered on the British Mediterranean Fleet, but their Navy lacked aggressiveness and they lost the opportunity for good.