0
They are shells fired from a gun with a bore of just under 1.5 inches.
122 mm
SP 152 MM, SP 122 MM, 122 MM Towed
122 mm = 4.80314 "
Direct Conversion Formula 122 mm*
1 in
25.4 mm
=
4.803149606 in
122 millimeters is 0.4 feet.