Short answers, pulled from the story.
Operation Grapeshot was the codename for the Spring 1945 Allied offensive in Italy, the final major Allied attack of the Italian Campaign. It was launched by the 15th Allied Army Group on the 6th of April 1945 and ended on the 2nd of May 1945 with the surrender of all Axis forces in Italy.
The offensive began on the 6th of April 1945 with a heavy artillery bombardment of the Senio river defenses. It concluded on the 2nd of May 1945 when the instrument of surrender signed at the Royal Palace of Caserta took formal effect.
Emissaries of Heinrich von Vietinghoff signed the instrument of surrender at the Royal Palace of Caserta on the 29th of April 1945. Marshal Rodolfo Graziani separately announced the unconditional surrender of the Italian Social Republic on the 1st of May 1945.
The Argenta Gap was a narrow strip of dry terrain, only 3 miles wide, between Lake Comacchio and a marshy area west of the lake. It was the key bottleneck the British Eighth Army needed to force in order to break into the Po Valley; by the 19th of April 1945 the 6th Armoured Division had pushed through it.
On the 19th of April 1945, the Italian National Liberation Committee for Northern Italy ordered a general insurrection. Partisans liberated Turin and Milan on the 25th of April, accepted the surrender of General Gunther Meinhold's 14,000 troops in Genoa on the 27th, and locked up a German garrison of 5,000 in Padua before Allied forces arrived on the 29th.
The 15th Army Group had a ration strength of 1,334,000 men, equivalent to just under 20 divisions. Axis forces as of the 9th of April comprised 21 weaker German divisions and four Italian National Republican Army divisions, with roughly 349,000 German and 45,000 Italian troops.