A question upon the lips of many people who research the K-3 marriage visa is: why do we use a different application form?
The K3 visa was initially designed as a way of getting spouses of American citizens to the United States in as fast a manner as possible. Back when the United States Citizenship and Immigration Service was referred to as the Immigration and Naturalization Service (INS), the classic I-130 application for an IR-1 or CR-1 Immigrant Spouse visa took as long as three years to adjudicate. This situation resulted in a massive backlog of petitions and is likely a reason underlying INS's reshuffle.
When filing for a marriage visa, the first phase is filing an I-130 petition. Should the couple decide to apply for a faster visa, then they can submit an application to USCIS. This phase can only occur after the initial petition has been received by the proper Immigration office.
In some ways the K3 visa (supplemental marriage visa) is similar to the V visa, which was designed to break the logjam of cases involving family members of those lawfully resident in the United States of America. At the time of this writing, the "V" visa category is being used less and less often because the statutory provision is effectively sun-setting.
This does not deal with the original question: why submit a K-1 visa application when a marriage visa is being sought? Put simply, it was probably simpler and less expensive to use the I-129f application form rather than create a completely new document to be used exclusively for the K3 marriage visa.
For those uninitiated in dealing with the United States Citizenship and Immigration Service, filing the proper paperwork is critical to obtaining an approval from the officers working for the Service.
It should always be remembered: lying to the United States government is not an effective means of getting a US visa. An approach such as this could result in a finding of legal inadmissibility and therefore cause more work, delay, and hassle in order to ultimately obtain the visa.
(Please note that nothing contained herein should be utilized as a substitute for legal advice. One should always contact an attorney for personalized legal consultation. A lawyer-client relationship should not be assumed to exist between the writer of this article and any reader.)