The date of this card is important. As I read it, it was drawn in early 1942 to be read by the Italian public. It is telling them that the Axis submarines have already reduced the Allied shipping to 30 million tons in Jan 42. If the rate of sinkings continue, the Allies will be defeated when the Axis reduces the Allied shipping to 20 million tons (expected in Jan 44). The note at the bottom states that the Allies are not fully replacing their losses. Each step is three months.
Pista! Jeff