Shell pierced steel plate...??

[starshell]

Hi all,
Bit of a long shot with this one, but I'm curious to know others opinions on this piece.

I took a trip to the Ypres salient to visit the old battlefield sites in November 2017, and whilst visiting Wytschaete Military cemetary (resting place of one of our relatives) discovered this piece of steel plate which was found on the fringes of Wytschaete village, beside the Kemmel-Wytschaete road. This road had been dug up to be resurfaced and had a continuous trench dug along one side to install a new drainage system.
The digging of the trench revealed this plate, along with rolls of German and British barbed wire, Pickets, timber shoring and lengths of narrow gauge railway and a belt buckle.
After breaking the ice with the construction manager with a crate of beers, I was allowed to pile the lot into the car (or at least most of it, space permitting).
Post cleaning, I'm trying to figure out what this plate might have been part of, and whether the hole is a shell strike or not. I'm of the opinion it is, but what do you think?
The plate has 2 straight edges, one at a 45 degree angle with what looks like 2 machined holes, possibly countersunk. (see 1st image..The top edge is the machined edge, the 45 deg edge is to the right where the metal is crumpled. All other holes are damage related.
The plate is 6mm thick but reduces to around 3-4mm in places.
I'd appreciate any ideas on this, I'm sure it could tell a few stories...
Many thanks in advance!

 

[reccetrooper]

I think that is a shell strike.

What are the length and width dimensions of the plate?

If the machined holes are not too corroded maybe you can measure them to see if they are a metric or imperial diameter.

 

[starshell]

Thanks reccetrooper,
The plate measures 26.5" long and 11" wide.
I initially thought the long curved edge was damage where the plate had been ripped from whatever it was attached to, but have now discovered it was probably cut that way. The edges are squared off. Judging by the way the 45 deg edge tails off, I think this plate is more or less its original size, with a small triangular piece missing from the 'crumpled' end.
The 2 holes are 1/2" diameter although I'm now highly doubtful they are countersunk. I going along the lines or rivet holes judging by the diameter. I can't see anyone using huge countersunk bolts for a piece like this? The mystery deepens...