what word links these: busy, honey, keeper?

Questions

Ships designed for the various operations involved in modern naval warfare?

Short, high-freuency radio waves lying roughly between very-high-freuency (infrared) waves & conventional radio waves (electromagnetic radiation; radio)?

Shrimps' hearts are where?

Sigmund Freud, founder of psychoanalysis, was born in what country?

as fit as a(n) __________?