  We say that a loop is unbreakable when it does not have nontrivial subloops.
While the cyclic groups of prime order are the only unbreakable finite groups,
we show that nonassociative unbreakable loops exist for every order n >= 5. We
describe two families of commutative unbreakable loops of odd order, n >= 7,
one where the loop's multiplication group is isomorphic to the alternating
group An and another where the multiplication group is isomorphic to the
symmetric group Sn. We also prove for each even n >= 6 that there exist
unbreakable loops of order n whose multiplication group is isomorphic to Sn.
