After listening, I read Makos' Spearhead: An American Tank Gunner, His Enemy, and a Collision of Lives in World War II and recommend it for the insight into daily life of a tanker on the West Front. The book features Smoyer's counterpart, Gustav Schaefer, a Panther tank gunner. Ultimately, both gunners meet up in front of the Cologne Cathedral in an encounter caught on film, then would meet again many years later on better terms.
Early in the book, an ambush of a column of Sherman tanks is described from Schaefer's point of view. I found this passage intriguing as the tables were turned on the Germans by the appearance of an M7 Priest which scored several direct hits on Schaefer's Panther, causing it to retreat then disabling it. I was surprised that the mobile artillery platform could engage Panthers and survive. It was not unheard of for artillery pieces to be used in direct fire mode, the Russians relied on this method early in the war and the German 88mm AA gun, while not technically artillery, was one of the most feared German weapons by both American tankers and infantry.
In my favorite WW2 simulation, the venerable Campaign Series, I live for a battery of Priests crossing into my line of sight and in range. American artillery fire is both abundant and deadly and there is definitely a satisfying element of revenge when the tables are turned. The game system assigns the M7 a very strong high explosive factor but limited armored piercing factors. In the book the Priest engaged the Panther at two miles away and was undetected until after scoring its first hit, which was a HE round of white phosphorus. Schaefer recalls another hit on the Panther's slanted front armor before the M7 was spotted. After two more hits in quick succession fissures started forming up and down the armor welds in the interior convincing the tank commander to retreat. In order to maneuver behind a grove of trees and out of the M7's LOS, the Panther's left side is exposed and the left track is hit. The Panther is still able to move but by the time the wheels roll off the last track the tank is safe behind cover.
In Campaign Series an M7 engaging a Panther from 8 hexes (two miles) will never get a retreat result and I'm not sure I would bother tweaking the combat system to allow for it but I'm glad to have read this account of what HE fire could do. The book mentions a statistic that most tank encounters on the West Front were won by the tank that was the first to spot and fire upon the enemy as what happened in this long range, one sided, duel.
Even though the M7 was outside of the Panther's "effective range" of about 1000 meters, if Schaefer had spotted the M7 first, a hit at two miles was not out of the question and the Panther's shells would not have an issue penetrating the M7's armor.
Update: excellent discussion with technical details over on The Miniatures Page forums concerning this subject matter.
From David Porter's Allied Tanks of World War II:
105mm Howitzer Motor Carriage (HMC) M7 Priest
Weight: 26.01 tonnes
Height 2.54 m
Engine: 298kW (400hp) Continental R975 C1 radial petrol
Speed: 42km/h (26mph)
1 x 105mm (4.1 in) M1A2 howitzer
1 x 12.7mm (0.5in) HMG
No information on armor but Infogalactic comes to the rescue with a link to the American Fighting Vehicle database where we find it was lightly armored (from 0.5 to 1.5 inch except by the lower front which was around 4.25 inches).
From the Encyclopedia of German Tanks of World War Two*:
Panzerkampfwagen V Ausf G (Sd Kfz 171).
I'll use the Ausf G model as it was produced from March 1944 to April 1945.
Weight: 45.5 tonns
Length: 8.86 meters
Width: 3.4 meters
Height: 2.98 meters
Engine: Mayback HL230P30
Speed: 46 kmhr
1 x 7.5cm KwK42 L/70
2 x 7.92mm MG34 (one in cupola, one lower front armor)
Armor (thickness in mm/angle in degrees) Front Side Rear Top/Bottom:
Turret: 110/11 45/25 45/25 16/84
Hull (upper): 80/55 50/30 40 & 16/90
(lower): 60/55 40/0 40/30 30-16/90
Gun mantlet: 100/round
There was an interesting note in the book when Clarence Smoyer was still a Sherman tank gunner in that feedback was distributed to all units that the Panther was vulnerable to the Sherman's gun from head on if the shell hit the Panther's gun mantlet but only at close range, i.e. <250 yards. Shells fired from the Sherman's 76mm gun were always ineffective against the thick / sloped frontal armor.
Note that the gun mantlet armor is thicker than the hull armor but the 55 degree slope of the hull armor gave it a greater relative thickness.
* Finally, Barnes and Noble is competitive with a book price against AMZN. Unfortunately, "currently not available online" but may be worth double checking if you are thinking of buying.
Over at Castalia House I have a post on an book released in 1905 right before the end of the Russian - Japanese War