Is it possible to file a patent application in the United States claiming foreign priority without a PCT application?
Yes. If another patent application has been previously filed in a foreign country by the applicant, and the applicant wants to claim priority back to the date of the prior foreign application, a U.S. application must be made within 12 months from the earliest date of the foreign filing (and six months in the case of a design patent). To make a priority claim under 35 U.S.C. ยง 119(b) to the prior foreign application, the applicant in the oath or declaration accompanying the U.S. application must state the country and date when the earliest application was filed, as well as identify any other applications made before the application on which priority is claimed. In addition, the applicant must provide a copy of the foreign application certified by the patent office of the country in which it was originally filed.
