according to this document
were 75mm guns with split trail, 31 caliber, firing a 5,9 kilo projectile, with a muzzle velocity of 518 m/s and a range of 7950 meters (table on page 47). On the next page they mention a total of 18 pieces found. The number of 11 is mentioned earlier on in the report on page 7 and a bit further down on page 16 the number of 7 x 75mm field gun "for general use in the fortress" are mentioned.
Hope this helps identifying the guns?