Do I actually need a US passport to return from UK travel with dual citizenship?

[joeronimo]

I've seen similar questions but the answers seem specific to the countries of travel and second country of citizenship, so:

I have a UK passport, and my Certificate of Naturalization, after taking the Oath last year. If I visit the UK, Switzerland, and Germany, and fly on my UK passport, will I need a US passport to re-enter the US? Or will my UK passport and US Certificate of Naturalization be sufficient?

[newacct]

The law (8 USC 1185(b)) says it is "unlawful" for a US citizen to enter and exit the US without bearing a US passport, unless otherwise allowed by regulations (which only deal with children crossing land borders and people with certain border crossing cards crossing land borders), but there is no penalty for violating this law. And if you manage to get to a US port of entry and can satisfactorily prove your US citizenship (e.g. with a Certificate of Naturalization and photo ID), they cannot deny you entry no matter what, even if you don't have a passport or other accepted document. They might just detain you to verify your citizenship and give you a lecture.

The real problem is, if you're flying to the US, the airline won't let you board. Airlines are required by the government to verify you have documents required for travel to the US before letting you board (see e.g. the Carrier Information Guide), and a Certificate of Naturalization is not among the accepted documents. For a US citizen, normally the only document you can present is a US passport. A British passport is not sufficient without a US visa or ESTA, and you should not be able to get those as a US citizen. (Although there are reports of dual nationals being able to get an ESTA.)

You can get a US passport quickly, either expedited, or directly at a passport agency if there is urgent travel. You should consider getting one before your travel. Alternately, you can get a US passport abroad at a US consulate in the country where you will be traveling, if there is time.