if I'm reading this right....these 737s have triple INS, GPS, TACAN, VOR, and ADF.
Unfortunately, P-3s are going into areas where NAVAIDs don't exist, GPS sh*ts itself on a regular basis, and INS's dump (INSes? INIi? what is the plural...). Yes, I'm sure the INS on a 737 makes a P-3's look...