Is a Lance Corporal (USMC) essentially the same as the Specialist rank in the Army?

It equals an E-3

It does not equate to any specialist rating the Army has, but rather steeped in tradition from Great Britain's Royal Marines, where we have borrowed many of their traditions. The Marine L/Cpl. "E-3", is in the transition role between PFC, and Coporal, where they have demonstrated proficiency in leadership, MOS, as well as basic infantry skills.

Whatever an E3 is in the army

Not the same

Yes

A LCpl is an E3 and a SP4 is an E4.

E3

um, no. A Lance Corporal is a time honored rank that is just pre-nco.

E3

PFC Army E-3 = L/Cpl E-3 Marine Corps pay grade wise but that is the only comparison you could make. SPC 4 is an E-4 and a Corporal in the Corps is an E-4 pay grade wise. There is NO comparison period. When the Army had Sp4cialist ranks E-4 through E-9, the designation made sense. The rank was an expansion of the Army 'Tech" ranks (T-Cpl -T-Sgt and T-6 (he equivalent of an Staff Sgt.). In essence the rank was for a specialize function/job with no responsibilities for operational duties although some assumed normal NCO responsibilities when needed.

The SPC-4 s the last remaining non-operational rank left. It's like the Army Medical Corps, doctors and nurses JAG and Navy Lawyers and doctors given an officers rank but not really. On the line any infantry Officer has the responsibility of command over any doctor or lawyer of equal rank.

In the Corps, as I mentioned before, an E-4 is a corporal and MUST perform and be qualified beefore getting prmoted whereas any Army PFC can become a SPC4 with T&G