Turns out Monitor may have been wearing a turret shield during the battle which was removed afterwards as it was deemed unnecessary. No photos are known to exist of Monitor before the battle clear enough to say ya or nay but from info it appears she was.
Changes how she looked a bit.
The computer-generated photograph on the left shows the Monitor’s turret as everyone remembers it . . .
while the one on the right shows how it would have looked originally, with its “Turret Shield” still in place.
Left: Illustration by Charles W. MacCord, inventor John Ericsson’s chief draftsman, showing details of the “Turret Shield,” intended to provide extra protection around the turret’s gun ports. Above: The left side of this drawing by Ericsson offers a bird’s-eye view of the shield in place in front of the gun ports.
Illustration by Charles W. MacCord, inventor John Ericsson’s chief draftsman, showing details of the “Turret Shield,” intended to provide extra protection around the turret’s gun ports. The left side of this drawing by Ericsson offers a bird’s-eye view of the shield in place in front of the gun ports.Original Plans Compiled In Drawings Of The U.S.S. Monitor
They have pieces of the armor and Ericsson's and other's writings speak of it.
On the day of the battle, 9 March 1862, Chief Engineer Alban C. Stimers, who was instrumental in the Monitor’s construction and served in the turret during the engagement, wrote to Ericsson reporting on the battle and his impression of the ship. He wrote, in part, “The turret is a splendid structure. I do not think much of the shield, but the pendulums are fine things.”20
Also, in the draft log of the Monitor in the National Archives, an entry for 21 March 1862 states: “From Meridian to 4 P.M. fine and pleasant weather,—light wind from E.S.E. and hauling to the S. At 2.30 the tugboat Young America came alongside and took on shore the shield of the turret.”21
Unfortunately, the log of the Young America for this time period is missing from the National Archives, so there is no information on exactly where the tug took the shield.
The fact the shield was in essence bolted on to the outside of the turret and thus easily removed may explain why it doesn't appears in official plans
A New Look for an Old Icon
https://www.usni.org/magazines/naval-history-magazine/2024/march/new-look-old-icon