Essentially yes: early model Shermans had a reputation for ammunition fires after shells cooked off when the tank was penetrated. Second-generation Sherman models like the M4A3 moved ammunition stowage from the vulnerable sponsons to to the floor of the tank, and encased them in a thinly-armoured bin that was filled with a mix of water and antifreeze. If a piece of hot shrapnel penetrated the bin and got through to the shells the ammunition would be soaked and not ignite.
Source:
Steven J. Zaloga, Panther vs Sherman: Battle of the Bulge 1944
"Dry" ammunition stowage
Early Sherman tanks had a rather poor method of ammunition stowage, with the rounds being stored high up in the tank's sponsons above the tracks. The bins the rounds were stored in were intially unarmored, and only the 1.5 inch (38 mm) side armor of the Sherman protected them from a hit. Catastrophic flash ammunition fires and explosions were very common on the early tanks; this was, and still widely is, often attributed to the gasoline tanks in the rear of the hull being hit, which is generally untrue. The "burn rate" when a dry stowage Sherman was hit was over 80 percent in some cases. For comparison, the "dry" Panzer IV was just as bad, if not worse, burning even slightly more readily. Wet ammunition stowage decreased the burn rate of Shermans to about 5 to 10 percent.
The dry stowage M4, M4A2, M4A3, and M4A4 stored their 75 mm ammunition as follows, looking at the tank from above. 97 rounds could be carried;
15 rounds in an unarmored rack in the front of the left sponson
17 rounds in an unarmored rack in the front of the right sponson
15 rounds in an unarmored rack in the rear of the right sponson
30 rounds in an unarmored rack behind the bow gunner underneath the turret
12 rounds arranged on clips around the back of the turret basket
8 rounds in an unarmored "ready rack" on the turret basket floor at the loader's feet
The M4A1 reduced this capacity to 90 rounds, as the curvature of the cast hull obstructed the left front ammunition rack, reducing its capacity to 8 rounds.
The 30-round hull floor rack was below the turret, and could only be accessed by the bow gunner. This rack was usually used as a "refill" to replenish the sponson ammunition racks. A steel mesh cover around the turret basket with a single exit hole meant that the turret often needed to be turned to allow the loader to retrieve ammunition from the sponson racks.^a If the turret was turned just right and the turret roof hatch blocked, the crew could be trapped; bad news in a fire. Wet stowage 75 mm Sherman variants dispensed with the mesh altogether.
This awkward design could often have near-fatal consequences, as was the case with tank commander Lieutenant Raymond Fleig and his battle with a Panther in the Hürtgen Forest. The round that Fleig pre-emptively had loaded in the gun was high-explosive and did no damage. The frightened Panther crew bailed out, but soon re-entered their tank. Realizing his mistake, Fleig's gunner hurriedly turned his turret to allow his loader to retrieve an armor-piercing round from the sponson, and shot the now-alerted and angry Panther in the side (the Panther, like the Sherman, stowed most of its ammunition in the sponsons) A massive explosion resulted, ripping open the side of the Panther and killing the whole crew.
In about August of 1943, one-inch thick exterior appliqué plates ("1" in the photo) and 1/4" armor plates and doors for the inside of the ammunition racks were devised and began to be installed at the various tank factories in order to protect the vulnerable ammunition racks of the Sherman. Appliqué plates were also installed in front of the driver's and bow gunner's protruding hatches to protect them, except on the M4A1.
| Manufacturer | Side appliqué date | Driver and bow gunner's appliqué date |
|---|---|---|
| American Locomotive Company | August 1943 | August 1943 |
| Baldwin Locomotive Works | August 1943 | August 1943 |
| Chrysler Defense Arsenal | August 1943 | August 1943 (N/A on M4 composites) |
| Federal Machine and Welder | August 1943 | August 1943 |
| Fisher Tank Arsenal | August 1943 | August 1943 |
| Ford Motor Company | August 1943 | August 1943 |
| Lima Locomotive Works | August 13, 1943 at S/N 30074 | N/A |
| Pacific Car and Foundry | August 1943 | Unknown |
| Pressed Steel Car Company | August 1943 | July 1943 (N/A on M4A1s) |
| Pullman Standard Car Company | Unknown | Unknown |
The patch on the left turret front ("2" in the photo) to cover up the "thin spot" where the turret casting was thinner in order to allow the turret traverse motor to operate properly was introduced in spring 1943.
In late 1943 and early 1944, a fundamental design transition took place in Sherman production. Initially, all Shermans had the "early" 56-degree angled hull with small driver and bow gunner's hatches that jutted out. In November 1943, near the end of its production, the M4A2(75) was the first variant to introduce the newly designed "late" 47-degree angled hull with a smooth glacis plate and larger hatches that allowed the driver and bow gunner to escape more easily. Earlier, injuries had resulted when crews tried to evacuate quickly through the small front hatches, and it was difficult to retrieve wounded or unconscious crew through them.
Oddly, the M4A2(75) introduced the 47-degree hull, but never had the wet ammunition stowage commonly associated with the new hull, so you still see them with appliqué plates. Nearly all later Sherman models from early 1944 on then used wet stowage in the late hull. The sole exception, the 105 mm howitzer-armed Shermans, had the late hull, but dry ammunition stowage. There were no "early hull" wet stowage Sherman tanks.
Dry stowage Sherman production
| Type | Date | Number built |
|---|---|---|
| M4 | July 1942-January 1944 | 6,748 |
| M4(105) | February 1944-March 1945 | 1,641 |
| M4A1 | February 1942-December 1943 | 6,281 |
| M4A2 | April 1942-May 1944 | 8,053 |
| M4A3 | June 1942-September 1943 | 1,690 |
| M4A3(105) | March 1944-April 1945 | 3,039 |
| M4A4 | July 1942-November 1943 | 7,499 |
| M4A6 | October 1943-February 1944 | 75 |
"Wet" ammunition stowage
"Wet" stowage consisted of a system where the main gun rounds were moved to racks on the hull floor. The rounds in each rack were surrounded by separate small containers of a mixture of water, ethylene glycol, and a rust inhibitor, known as "Ammudamp." As /u/RobWithOneB said, the rounds aren't actually "wet," the rounds are just separated by the small liquid containers. When the ammunition rack was hit, the logic was that the liquid would spill out, quenching any fires, similar to flooding the magazine on a warship. These pictures show an individual 75 mm 10-round "wet" ammunition rack separated into two parts; first the three liquid containers separate of the rack, and then the rack itself.
76 mm wet stowage Shermans
The first Sherman variant to incorporate wet stowage was the M4A1(76)W, beginning in January 1944. This variant could hold 71 76 mm main gun rounds in three locations:
A 35-round (7 5-round racks) arrangement on the left side of the propeller shaft behind the driver
A 30-round (6 5-round racks) arrangement on the right side of the propeller shaft behind the bow gunner. This rack arrangement was shorter due to the position of the floor escape hatch.
6 rounds in an armored "ready rack" on the turret basket floor at the loader's feet
This picture shows the left-side ammunition racks of an M4A3(76)W; the caps for the liquid containers can be seen at the sides of each rack, and between the second and third rounds. The M4A1(76)W, M4A2(76)W and M4A3(76)W shared the same ammunition stowage arrangement. The 76 mm Shermans only had "half" a turret basket to allow the loader easier access to the larger ammunition.
75 mm wet stowage Shermans
In February of 1944, the 75 mm variant of the Sherman joined the party with the M4A3(75)W. This variant could hold 104 main gun rounds, in comparison to the 90 to 97 rounds of the earlier 75 mm dry stowage Sherman. The ammunition stowage was as follows;
A 50-round (5 10-round racks) arrangement on the left side of the propeller shaft behind the driver
A 50-round (5 10-round racks) arrangement on the left side of the propeller shaft behind the bow gunner
4 rounds in an armored "ready rack" on the turret basket floor at the loader's feet
This picture shows the rows of 10-round ammunition racks on the hull floor of the M4A3(75)W. The M4A3(75)W, like earlier 75 mm models, had a full turret basket floor, but the loader now had flaps that he could flip up to allow him access the rounds directly below. The M4A3E2 "Jumbo" was converted from a standard M4A3(75)W Sherman hull, and hence had the same ammunition stowage arrangement.
Wet stowage Sherman production
| Type | Date | Number built |
|---|---|---|
| M4A1 | January 1944-July 1945 | 3,426 |
| M4A2 | May 1944-May 1945 | 2,915 |
| M4A3(75) | February 1944-March 1945 | 3,071 |
| M4A3(76) | March 1944-April 1945 | 4,542 |
| M4A3E2 | May-July 1944 | 254 |
a: Prior to D-Day, several modifications were made to the ~1,400 Sherman tanks already in the UK that were preparing for the invasion. Hull and turret appliqué armor plates, as well as the armor plates and doors for the sponson racks were fitted to tanks that did not already have them. This really didn't solve the fire problem, as the main gun rounds were not yet moved to the floor or surrounded by the liquid containers. The mesh around the turret basket was removed to increase crew survivability. The 12 vulnerable rounds around the back of the turret basket were removed also. A smoke mortar, via a British order, was also installed in the left front of the turret.
Sources:
Armored Thunderbolt: The US Army Sherman in World War II, by Steven J. Zaloga
Sherman: Design and Development, by Patrick Stansell and Kurt Laughlin
M4 Sherman at War (Zenith Press)
M4 (76mm) Sherman Medium Tank 1943-65, by Steven J. Zaloga
A Dark and Bloody Ground: The Hürtgen Forest and the Roer River Dams 1944-1945, by Edward G. Miller