Whenever the US starts talking about weapons of war, I tend to focus on the details. I have to say there are more than a few of those missing when it comes to what the United States plans to do in Yemen.

We know the US is sending the USS Theodore Roosevelt to patrol off the coast. That will bring the total to eight US warships in the area.
The announcement and the leaks from the Pentagon were straight out of their usual playbook. On the record, officials said the ship was going. Then came the off the record, not for attribution reporting. Unnamed defence sources told reporters the ships were going in order to “intercept potential shipments of Iranian weapons to the rebels”.
That allowed officials to dial it back a bit the following day, without looking like they actually were. You can’t go back to an unnamed official and say he lied.
The point is the story was out there. The message had been sent to Iran: the US could try to block them.
There are a couple of issues that need to be addressed. First and foremost, what evidence does the US have that Iran is in fact shipping weapons? We’ve heard the White House press secretary Josh Earnest say they have evidence, but he did not reveal what it is. That seems important.
Unanswered questions
The US won’t answer the basic question of whether they plan to board any ships. The bigger question should be - can they? What legal authority does the US have to intervene off the coast of Yemen?
White House officials didn’t have to answer that question, surprisingly. When they talk about why the warships are going it is to keep “shipping lanes” open.
They repeatedly talked about the United Nations Security Council arms embargo. So let’s take a look at resolution UNSCR 22116 – it says:

14. ...all Member States shall immediately take the necessary measures to prevent the direct or indirect supply, sale or transfer to, or for the benefit of Ali Abdullah Saleh, Abdullah Yahya al Hakim, Abd al-Khaliq al-Huthi, and the individuals and entities designated by the Committee …, and those acting on their behalf or at their direction in Yemen.”
To be clear, people were sanctioned, but the Obama administration believes there is a weapons embargo to the entire Houthi group because they are "acting on their behalf". 

We don’t know if the US is going to use that as legal justification to board ships off the coast of Yemen. They haven’t had to answer that question, or as it turns out, pretty much any question about what the US Navy will be doing there.

http://www.aljazeera.com/news/2015/04/analysis-man-save-yemen-150413113949455.html