This is Kipling in full jingoistic mode, beating the drum for British naval supremacy. The children who were this poem’s original audience were children of the Empire – an empire that included Hong Kong and Bombay as well as Hobart, Melbourne, Quebec and Vancouver – and Kipling wanted to make sure they knew it.
What’s interesting is the terms in which he gets the message across. British imperialism, and the military strength needed to support it, are justified on the most basic terms possible: we need the warships, because we need to be able to send the “big steamers” to India, Australia and Canada; and we need to do that because we need to eat. We need to rule the world because we’re so weak, in other words. It’s reminiscent of the patriotic mindset Anthony Barnett describes in this piece, in which Britain is at once a humble underdog (“It is a nasty world and, surrounded by it, we are but a modest, embattled island nation.”) and a world superpower (“Our goodness gives us an inner strength and integrity which, with our long experience, means we can suggest with all due modesty that the world needs our leadership”).
The poem gets noticeably darker as it goes on; the last verse, and the last line in particular, spells out what’s at stake in no uncertain terms. Interestingly, the last verse appears to be addressed to an audience of adults as well as children – at least, we assume that the people who carve joints of meat aren’t the same as the ones who suck sweets and nibble biscuits.
A hundred years on, of course, Britain’s still a net importer of food, but we manage to get by without imperial supremacy; we’ve got globalisation instead.