On Monday, Air Chief Marshal Angus Houston, who heads the agency co-ordinating the search, said it was time to deploy the Bluefin-21 to begin its search of the sea floor. It set off on its first mission on Monday night." After completing around six hours of its mission, Bluefin-21 exceeded its operating depth limit of 4,500m and its built in safety feature returned it to the surface," the Joint Agency Co-ordination Centre said in a statement.

Its built? What is it?

I may understand the meaning of safety feature, but it is very difficult to figure out what does "its built" mean.


The phrase built in (often hyphenated when used as an adjective: built-in) refers to something installed into a product at the factory.

For example:

  • an automobile might have built-in airbags
  • a computer might have extra RAM built in (meaning you don't have to add it yourself)

In your sentence, the Bluefin-21 was designed so that, instead of exceeding its maximum depth, it would return to the surface. This feature was built into its software, apparently. Judging by this news story, that seems to have been a smart design decision.

The context of your question reminds me of Asimov's three Laws of Robotics.


It’s an included feature (additional construction), which makes the device return to the surface.

  • what does built here mean? Different from feature? A million thanks.
    – user5036
    Apr 15 '14 at 10:07
  • 1
    it's built-in, which means included (incorporated) Apr 15 '14 at 10:08

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