What was the US monetary policy like in the 70s? Today the US inflation target is roughly 2%.
However in 1974 the inflation rate was 11% and in 1980 it was 13.5%.
What monetary policy did they follow at that time that allowed the inflation to rise to these levels?

Looking at the U.S. National Unemployment Rate:

we see that it had a local minima of 4.6% in october 1973 and another one at 5.7% in June 1979.
In the 70s U.S. Fed policy was in disarray and Fed was not following consistent monetary policy (at least not by present day standards). Generally monetary scholars characterize the Fed monetary policy in the 70s as &quot;go-stop&quot; policy. As argued by Goodfriend (2007):

At the heart of the disarray in monetary policy practice in the 1970s was the
tendency for a central bank like the Federal Reserve to pursue “go-stop” monetary
policy. Go-stop policy was a consequence of a central bank’s inclination to be
responsive to the shifting balance of public concerns between inflation and unemployment. The central bank would stimulate employment in the “go” phase of the
cycle until the public became concerned about rising inflation. Then aggressive
interest rate policy initiated the “stop” phase of the policy cycle to bring inflation
down, while unemployment rates moved higher with a lag. Public support for  interest rate increases evaporated once the unemployment rate began to rise, so it
was politically difficult to reverse a higher inflation rate.


Wage and price setters learned to take advantage of tight labor and product
markets in the “go” phase of the policy cycle to make increasingly inflationary
demands, which neutralized the monetary stimulus. As a result, central banks
became ever more expansionary in the pursuit of low unemployment. Lenders
demanded ever-higher inflation premia in bond rates which moved higher and
fluctuated widely. By pursuing low unemployment and fighting inflation only when
it became the predominant public concern, central banks then increased the
volatility of both inflation and output.


Other factors contributed to the disarray in monetary policy in the 1970s. In
the 1960s, the widespread belief in a long-run Phillips curve trade-off between
inflation and unemployment inclined central banks to allow inflation to drift
upward in the hope of achieving a permanently lower level of unemployment. Also,
the productivity growth slowdown of the 1970s caused central banks like the
Federal Reserve to overestimate noninflationary potential output (Orphanides,
2003). Oil price shocks that occurred in 1973 and 1979 – 80 worsened the inflation
problem, although neither of the oil price shocks produced the 3 percentage point
increase in U.S. inflation that occurred in the 18 months prior to Paul Volcker
becoming Fed chairman in August 1979.

Consequently, the Fed was pursuing generally quite erratic loose monetary policy with occasional abrupt tightening.