A subcommittee of the United States Senate held hearings in 1912 to investigate the RMS Titanic disaster. (https://www.senate.gov/reference/reference_item/titanic.htm Why did the Senate do so, given that it was a British ship, crewed mostly by British citizens, operated by the White Star Lines (a British company), and (on account of the disaster) the ship never visited the United States at all? Granted, many American citizens died on the ship, but the fact that hearings into this incident seem out of character for the limited government philosophy that I understand to have prevailed at the time.
The US was very much in the best position to inquire about the sinking in the following days after the disaster, as all the survivors were ferried to New York City on the RMS Carpathia, so the US was most able to interview these surviving passengers and crew while they were all in one place, before they dispersed and returned to their homes. The US also had an interest because of the international attention gained by the sinking of the Titanic, a maritime disaster in where nearly 70% of the ships crew and passengers died. The US Senate wanted to investigate to see what went wrong to cause such an exceptionally high morality rate in the sinking of a passenger liner, and to take measures to prevent such a disaster from happening again with new regulations the counter the unpreparedness or even flat-out neglect on the part of the White Star Line in the face of the tragedy.
The investigation was proposed to the Senate by US Senator William Alden Smith, who had a previous record sponsoring work safety regulations by sponsoring bills that regulated the railroad industry, he was elected on a platform of cracking down on workplace safety and proposing regulations, so looking deeper into a major maritime disaster was something he wanted to look closely into as part of his platform.
The 18 days of questioning from the Senate committee of the survivors and crew did reveal much information regarding the disaster. The findings concluded that the Titanic did receive warnings of ice in the area but the ship did not slow down its speed in accordance with the warnings. The number of lifeboats on board was in accordance with standing law, but still was not enough to carry all the passengers and crew (before this the purpose of lifeboats was to ferry people from a sinking ship to a rescue ship, not to carry the entire ship's passengers all at once). The lack of lifeboat drills for the crew which resulted in disorganized loading and even lowering the lifeboats before they were at full capacity (hell, one lifeboat even lowered with only 12 people on board!). Along with other findings such as the SS Californian's close proximity to the Titanic (so close that the Caliornian's crew did spot the distress rockets) but failed to act or approach the Titanic. Some members of the Californian testified that they thought the rockets they spotted were a show of fireworks rather than distress, and no attempt was made by the Californian to contact the Titanic by telegraph.
The inquiries resulted in major changes to maritime procedures after the White Star Line was found in "a state of absolute unpreparedness" in the wake of the sinking. Lifeboat numbers would be increased to accommodate all passengers and crew, ships were to slow their speed upon warnings of ice along with posting additional lookouts on watch. Rockets were to only be used exclusively in times of distress to avoid confusion. Lifeboat drills would be mandatory on all crews to better organize an evacuation.
To put it short, the US sought these inquiries because they were in the best position to do so with the survivors and crew being in New York City in the immediate aftermath of the disaster, and could question them before they dispersed and returned to their homes. The US also had an interest in know how this especially deadly sinking even happened to prevent similar disasters from happening both to US ships and other vessels crossing the Atlantic.
If you want the full text of the inquiry as well as the conclusions and responses made as a result, the documents can be found here. I'll also recommend taking a look into Unsinkable: The Full Story of the RMS Titanic by Daniel Allen Butler.
The White Star Line was predominantly owned by JP Morgan, the owners of Titanic and the other Olympic class liners (Olympic and Britannic)
Even though White Star line and all their vessels were registered generally in Liverpool, UK The Americans had a lot of influence in the company. They even say Titanic was primarily designed for American attitudes and tastes and least in first class. This could be evident in the signage for the first class areas. For example the lifts onboard were known as elevators on the Olympic class, rather than the correct British term of a lift.