  It is shown theoretically that ferromagnetic superconductors, UGe$_2$, URhGe,
and UCoGe can be described in terms of the A-phase like triplet pairing similar
to superfluid $^3$He in a unified way, including peculiar reentrant, S-shape,
or L-shape $H_{\rm c2}$ curves. The associated double transition inevitable
between the A$_1$ and A$_2$-phases in the $H$-$T$ plane is predicted, both of
which are characterized by non-unitary state with broken time reversal symmetry
and the half-gap. UTe$_2$, which has been discovered quite recently to be a
spin-polarized superconductor, is analyzed successively in the same view point,
pointing out that the expected A$_1$-A$_2$ transition is indeed emerging
experimentally. Thus the four heavy Fermion compounds all together are entitled
to be topologically rich solid state materials worth further investigating
together with superfluid $^3$He A-phase.
