At the Electron Ion Collider Deep Inelastic Scattering on deuterons combined with proton and tagging would complete control of the initial state and allow detailed measurements of the neutron and proton parton functions and their spin dependence. At the LHC proton tagging of diffractive, pp and pA events allow for complete control of the kinematics of the initial state. Similarly neutron tagging of incoherent vector meson production allows the photon direction to be determined and so allows for the measurement of low x gluon distribution functions over a range of Bjorken X. Both colliders impose severe constraints on the resolution, speed and radiation hardness of the forward systems. This talk will discuss possible implementations of such detectors and map out the R&D needed to enable the physics measurements described above.
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