This is a 1/350th scale after deckhouse and tear drop shaped gun tub for the Trumpeter or Tamiya 1/350th USS Fletcher-class model.
This version represents that fitted to the USS Fullam, and similar, with an integrated Mark 49 gun director included. The mounting hole for the aftermarket, modeler supplied 40mm Bofors is 1 mm in diameter. The holes in the deckhouse sides represent locations where hatches would normally be. Simply apply your favorite aftermarket photoetched hatches there. Each Fletcher was almost unique in the myriad types of doors and hatches it carried, so to ensure accuracy its probably best that the modeler select the hatch or door that best replicates that carried by the Fletcher that he or she is building.
Note that on Fullam, the cylinder that the director sat atop extended downwards aways. This was not always the case. If the Fletcher that you are modeling carried the Mark 49 in a tear drop gun tub but the cylinder was shorter, then please have a look at te second version of this part, where the cylinder is much shorter.
Clean the part by soaking it in lukewarm soapy water and then CAREFULLY scrubbing it with a soft toothbrush or similar. Be carefully, as the splinter shielding is just 0.3 mm thin and is easily damaged. Acrylic modeling paints are probably best. Consider painting the interior of the part, as well, to reduce light transfer through the otherwise mostly clear part. This will reduce the need to overpaint the exterior, allowing the parts finer details to not be covered over with paint.